IBRARY    OF   THE    UNIVERSITY   OF    CALIFORNIA 


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IVERSITY   OF   CALIFORNIA 


LIBRARY   OF  THE    UNIVERSITY 


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LIBRARY    OF   THE    UNIVERSITY 


.  A   GUIDE 

TO    THE 

SCIENTIFIC  KNOWLEDGE 

OF    THINGS    FAMILIAR; 

BY 

REV.  DR.  BREWER, 

TRINITY    HALL,    CAMBRIDGE, 

Head  Master  of  King's  College  School,  Norwich— in  union  with  King-* 
College,  London. 


<Earefull£  3&ebfsett,  aitfc  aTjajjteto  for  use  fit 
antJ  Schools  of  tfje  Simteti  States. 


NEW  YORK- 

C.   S.  FRANCIS  &  CO.,  252  BROADWAY, 
BOSTON: 

J.    H.   FRANCIS,    128   WASHINGTON    ST. 

1851. 


Entered,  according  to  Act  of  Congress,  in  the  year  1850, 

BY  C.  S.  FRANCIS  &  Co., 

in  the  Office  of  the  Clerk  of  the  District  Coiul  of  the  Southern 
District  of  New  York. 


PRINTED    BY 

MUNROE  &  FRANCIS, 

Boston. 


iff  I 


PREFACE. 


No  science  is  more  generally  interesting  than 
that  which  explains  the  common  phenomena  of 
life.  We  see  that  salt  and  snow  are  both  white, 
a  rose  red,  leaves  green,  and  the  violet  a  deep 
purple  ;  but  how  few  persons  ever  ask  the  reason 
why !  We  know  that  a  flute  produces  a  musical 
sound,  and  a  cracked  bell  a  discordant  one — that 
fire  is  hot,  ice  cold,  and  a  candle  luminous- — that 
water  boils  when  subjected  to  heat,  and  freezes 
from  cold  ;  but  when  a  child  looks  up  into  our  face 
and  asks  us  "  why  " — how  many  times  is  it  silenced 
with  a  frown,  or  called  "very  foolish  for  asking 
such  silly  questions  !"  The  object  of  the  present 
book  is  to  explain  about  2000  of  these  questions 
(which  are  often  more  easily  asked  than  answered) 
in  language  so  simple  that  a  child  may  understand 
it,  yet  not  so  childish  as  to  offend  the  -  scientific. 
In  order  to  secure  the  strictest  accuracy  in  the 
answers,  the  most  approved  modern  authors  have 
been  consulted,  and  each  edition  has  been  submitted 
to  the  revision  of  gentlemen  of  acknowledged  repu- 
tation for  scientific  attainments.  Sincere  thanks 
are  due  to  the  KEV.  A.  BATH  POWER,  M.  A., 
and  to  ROBERT  JAMES  MANN,  ESQ..  M.  R.  C.  S.,  of 
Buxton,  for  their  most  careful  revisions  of  the 
whole  book,  for  many  excellent  hints  and  useful 
additions.  In  conclusion,  the  almost  unparalleled 
success  of  this  little  volume,  of  which  25,000  copies 


VI  PREFACE. 

have  been  printed,  since  the  year  1848,  is  an  in- 
controvertible proof  of  its  acceptability;  and  has 
induced  the  author  to  spare  neither  labor  nor  ex- 
pense to  render  his  "  Guide  to  the  Scientific  Know- 
ledge of  Things  Familiar"  instructive  and  amusing 
to  the  young,  as  well  as  to  those  of  maturer  life. 

To  teachers  of  schools  it  may  be  advisable  to 
state,  that,  as  every  question  has  been  again  and 
again  submitted  to  a  most  rigid  investigation,  no 
material  alterations  will  be  made  in  future  editions. 


A  remarkable  instance  came  before  the  author  a  few 
months  since  of  the  statement  made  in  the  early  part  of 
this  preface.  The  conversation  was  about  smoke — why  it 
was  black,  and  not  white  like  the  fine  dust  of  lime.  A 
little  child  who  was  present,  asked,  "Why  is  the  kettle  so 
black  with  smoke  V  Her  papa  answered,  "  Because  it 
has  been  on  the  fire ;"  "  But "  (urged  the  child)  "  what  is 
the  good  of  its  being  black!"  The  gentleman  replied, 
"  Silly  child — you  ask  very  foolish  questions — sit  down 
and  hold  your  tongue."  He  might  have  read  pp.  185, 
and  186,  and  answered  the  child  more  discreetly. 


THE  AMERICAN  PUBLISHERS  offer  their  revised  edition 
of  this  useful  book,  in  full  confidence  that  it  will  meet 
with  an  equal  and  universal  acceptance  both  in  families 
and  schools,  throughout  this  country.  They  believe  it 
will  be  found  to  contain  an  amount  of  useful  information 
never  before  collected  in  a  shape  so  convenient  for  study, 
and  so  easy  for  reference. 


SUBJECTS   OF  THE   CHAPTERS. 


PART  I.-HEAT. 

PAOB 

Introduction 9 

I. — The  SUN  a  source  of  heat    .       .       .       .       10 
II. — ELECTRICITY  a  source  of  heat .       .       .       11 

II.— Thunder  and  lightning  11—36 
III. — CHEMICAL  ACTION  a  source  of  heat  .  36 
III. — Chemical  action  .  .  36 
IV. — Combustion  .  .  .39 
V. — Smoke  and  smoky  chimneys  62 
VI. — Lamps  and  candles  .  .  74 
VII.— Animal  heat  ...  83 
VIII. — MECHANICAL  ACTION  a  source  of  heat  94 
VIII.— Percussion  ...  94 
IX.— Friction  ....  97 
X. — Condensation,  or  Compression  100 

XI. — EFFECTS  OF  HEAT    .       .  .       .       .102 

XI. — Expansion  .        .        .  .102 

XII. — Same  subject  continued  .     117 

XIII.— Liquefaction    .        .  .121 

Vaporization  (clouds)  .    121 

XIV.— Evaporation     .        .  .147 

XV. — COMMUNICATION  OF  HEAT  .       .       .     155 

XV.— Conduction         .        .  .155 

XVI.— Absorption       .        .  .173 

XVII.— Reflection       .        .  .179 

XVIII.— Radiation  (dew)  .     182 

XIX.— Convection  (boiling)  .    213 


PART  II.-AIR. 


PADS 

XX. — THE  ATMOSPHERE 219 

Gases     The  Blood.     Rust.     Tarnish,  &c. 
XXI. — CARBONIC  ACID  GAS      .       .       :       .     238 

Froth.     Effervescence.     Fermentation,  &c. 
XXII. — CARBURETTED  HYDROGEN  GAS  .       .261 

Fire-damp.     Safety  lamp,  &c. 

XXIII. — PHOSPHURETTED  HYDROGEN  GAS  .     265 
Ignis  Fatuus.     Ghosts,  Ac. 

XXIV.— WIND     .:>;',.       .       .       .268 

XXV.— BAROMETER .296 

Ten  Special  Rules,  &c. 

XXVI.— SNOW.     HAIL.     RAIN      ...     309 
XXVII.— WATER        .       .       .       .       .       .319 

XXVIII.— ICE 325 

Freezing  mixtures.     Frost.     Swimming,  &c. 

XXIX.— LIGHT 338 

Reflection.     Telescopes.    Refraction. 

Spectacles.    Rainbows.     Color. 
XXX.— SOUND .377 

Ear  trumpets.     Echoes,  &c. 
PART  III. -MISCELLANEOUS. 

Attraction.  Anti-putrescents.  Dreams.  Color. 
Ink.  Iron.  Bread.  Horn.  India-rubber. 
Starch.  Meat.  Butter.  Mirrors.  Bricks. 
Milk.  Steel.  Manure.  Soap,  etc.  ...  387 

Antidotes  to  Poisons 452 

Glossary 454 

Index 455 

Index  to  Part  III.— Miscellaneous  Ques- 
tions .  .  485 


PART  I. 
HEAT. 

INTRODUCTION. 

Q.       What  is  HEAT  1 

A.     The  sensation  of  warmth. 

Q.      How  is  this  sensation  produced  ? 

A.  When  we  touch  a  substance  hot- 
ter than  ourselves,  a  subtile  invisible 
stream  flows  from  the  hotter  substance, 
and  produces  on  our  nerves  the  "  sensa- 
tion of  warmth." 

Q.  What  is  that  "subtile  invisible  stream" 
CALLED,  which  flows  from  the  hotter  substance  ? 

A.  CALO'RIC.  Caloric,  therefore,  is 
the  agent,  which  produces  the  sensation 
of  warmth;  but  HEAT  is  the  sensation 
itself. 

Q.  What  are  the  four  principal  SOURCES  of 
heat? 

A.  1.—  The  Sun.  2.— Electricity. 
3. — Chemical  Action ;  and  4. — Mechan- 
ical Action. 

(1*)  9 


10  HEAT. 

Q.       What  are  the  principal  EFFECTS  of  heat  ? 
A.     Expansion,  Liquefaction,  Vapor- 
ization, and  Ignition. 


CHAPTER  I. 

THE    SUN. 

Q.       What  is  the  PRINCIPAL  source  of  heat  ? 
A.     The  SUN. 

Q.  Why  do  BURNING  GLASSES  set  fire  to  sub- 
stances submitted  to  their  power  ? 

A.  Because,  when  the  rays  of  the 
Sun  pass  through  the  burning  glass,  thejr 
are  bent  toward  one  point,  called  the 
•"  focus;"  in  consequence  of  which,  the 
light  and  heat  at  this  point  are  very 
greatly  increased. 

Q.  Why  is  there  a  DARK  RIM  round  this 
focus  ? 

A.  Because  the  rays  of  light  are 
bent  from  the  rim  into  the  focus;  and, 
as  the  rim  is  deprived  of  these  rays,  it  is 
darkened. 

Q.      Are  ALL  the  rays  bent  into  one  point  ? 

A.  Not  quite  all :  and,  therefore,  the 
rim  round  the  focus  is  not  quite  black, 
but  only  dim. 


ELECTRICITY.  11 

CHAPTER  II. 

ELECTRICITY. 

Q.       What  is  the  SECOND  chief  source  of  heat  ? 

A.     ELECTRICITY. 

Q.       What  is  LIGHTNING  ? 

A.  Lightning1  is  accumulated  elec- 
tricity discharged  from  the  clouds. 

Like  that  from  a  "  Leyden  jar." 
Q.       What  CAUSES  the  discharge  of  an  electric 
cloud  ? 

A.  When  a  cloud,  overcharged  with 
electric  fluid,  approaches  another  which 
is  undercharged,  the  fluid  rushes  from 
the  former  into  the  latter,  till  both  con- 
tain the  same  quantity. 

N.  B.  It  is  generally  supposed  that  there  are  two  dif- 
ferent sorts  of  Electricity — one  Vitreous,  and  the  other 
Resinous. 

Q.  Is  there  any  OTHER,  cause  of  lightning,  be- 
sides the  one  just  mentioned  ? 

A.  Yes  ;  sometimes  mountains,  trees, 
and  steeples,  will  discharge  the  light- 
ning from  a  cloud  floating  near ;  and 
sometimes  electric  fluid  rushes  out  of  the 
earth  into  the  clouds. 

Q.       What  produces  ELECTRICITY  in  the  CLOUDS  ? 

A.  1st — The  evaporation  from  the 
earth's  surface  ; 


12  ELECTRICITY. 

2dly — The  chemical  changes,  which 
take  place  on  the  earth's  surface  ;  and 

3dly — Currents  of  air  of  unequal 
temperature,  which  excite  electricity  by 
friction,  as  they  pass  by  each  other. 

Q.  How  HIGH  are  the  LIGHTNING  CLOUDS 
from  the  earth  ? 

A.  Sometimes  they  are  elevated  4 
or  5  miles  high  ;  and  sometimes  actually 
touch  the  earth  with  one  of  their  edges : 
but  they  are  rarely  discharged  in  a  thun- 
der storm,  when  they  are  more  than 
700  yards  above  the  surface  of  the 
earth. 

Q.      How  high  are  the  clouds  GENERALLY  ? 

A.  In  a  jine  day,  the  clouds  are 
often  4  or  5  miles  above  our  heads  ;  but 
the  average  height  of  the  clouds  is  from 
li  to  2  miles. 

Q.       Why  is  lightning  sometimes  FORKED  ? 

A.  Because  the  lightning-cloud  is  a 
long  way  off ;  and  the  resistance  of  the 
air  is  so  great,  that  the  electrical  cur- 
rent is  diverted  into  a  zig-zag  course. 

Q.  How  does  the  resistance  of  the  air  make  the 
lightning  zig-zag  ? 

A.  As  the  lightning  condenses  the 
air  in  the  immediate  advance  of  its  path, 
it  flies  from  side  to  side,  in  order  to  pass 
where  there  is  the  least  resistance. 


LIGHTNING.  13 

Q.  Why  are  there  sometimes  TWO  flashes  of 
forked  lightning  at  the  same  moment  ? 

A.  Because  (in  very  severe  storms) 
the  flash  will  divide  into  two  or  more 
parts  ;  each  of  which  will  assume  the 
zig-zag  form. 

Q.      Why  is  the  FLASH  sometimes  quite  STRAIGHT  ? 

A.  Because  the  lightning-cloud  is 
near  the  earth ;  and,  as  the  flash  meets 
with  very  little  resistance,  it  is  not 
diverted;  (in  other  words)  the  flash  is 
straight. 

Q.       What  is  SHEET  LIGHTNING  ? 

A.  Either  the  reflection  of  distant 
flashes  not  distinctly  visible ;  or  else 
several  flashes  intermingled. 

Q.  What  OTHER  for m  does  lightning  occasion- 
ally assume  ? 

A.  Sometimes  the  flash  is  globular  ; 
which  is  the  most  dangerous  form  of 
lightning. 

Q.  What  are  those  BALLS  of  FIRE,  which 
sometimes  fall  to  the  earth  in  a  thunder-storm  ? 

A.  Masses  of  explosive  gas,  formed 
in  the  air :  they  generally  move  more 
slowly  than  lightning. 

Q.  Why  are  BALLS  of  FIRE  so  very  DANGER- 
OUS? 

A.     Because,   when   they  fall,   they 


14  ELECTRICITY. 

explode  like   a  cannon  ;  'and  occasion 
much  mischief. 

Q.  Do  these  BALLS  of  FIRE  ever  run  along  the 
ground  ? 

A.  Yes  ;  sometimes  they  run  a  con- 
siderable way  along*  the  ground,  and 
explode  in  a  mass  : 

At  other  times  they  split  into  nume- 
rous smaller  balls,  each  of  which  explodes 
in  a  similar  manner. 

Q.  What  MISCHIEF  will  these  balls  of  fire 
produce  ? 

A.  They  will  set  houses  and  barns 
on  fire  ;  and  kill  all  cattle  and  human 
being's,  which  happen  to  be  in  their 


Q.  Why  does  LIGHTNING  sometimes  KILL  men 
and  beasts  ? 

A.  Because  (when  the  electric  cur- 
rent passes  throug-h  a  man  or  beast)  it 
produces  so  violent  an  action  upon  the 
nerves,  that  it  destroys  life. 

Q.  WHEN  is  a  person  struck  DEAD  by  light- 
ning^ 

A.  Only  when  his  body  forms  a  part 
of  the  lightning's  path  ;  i.  e.  when  the 
electric  fluid  (in  its  way  to  the  earth) 
actually  passes  through  his  body. 

Q.  Why-  are  MEN  sometimes  MAIMED  by  light* 
ning  ? 


THUNDER;  15 

A.  Because  the  electric  fluid  pro- 
duces an  action  upon  the  nerves  sufficient 
to  injure  them,  but  not  to  destroy  Ufe. 

Q.       What  is  THUNDER  ? 

A.  The  noise  made  by  the  concussion 
of  the  air  when  it  closes  again,  after  it 
has  been  parted  by  the  lightning*  flash. 

A  part  of  the  noise  is  owing  to  certain  physical  and  chem- 
ical changes  produced  in  the  air  by  the  electric  fluid. 

Q.  Why  does  LIGHTNING  part  the  air  through 
which  it  passes  ?  it  does  not  part  a  rod  of  iron. 

A.  As  iron  is  a  conductor,  it  allows 
the  fluid  to  pass  freely  over  it ;  but  air 
(being*  a  non-conductor)  resists  its  pas- 
sage. 

Q.  Why  is  THUNDER  sometimes  ONE  VAST 
CRASH  ?  •• 

A.  Because  the  lightning-cloud  is 
near  the  earth  ;  and  as  all  the  vibrations 
of  the  air  (on  which  sound  depends) 
reach  the  ear  at  the  same  moment,  they 
seem  like  one  vast  sound. 

Q.  Why  is  the  PEAL  sometimes  an  IRREGULAR, 
broken  ROAR  ? 

A.  Because  the  lightning-cloud  is  a 
long  way  off;  and  as  some  of  the  vibra- 
tions of  the  air  have  much  further  to 
travel  than  others,  they  reach  the  ear  at 
different  times,  and  produce  a  continuous 
sound. 


16  THUNDER. 

Q.       Which  vibrations  will  be  soonest  heard? 

A.  Those  produced  in  the  lowest  por- 
tions of  the  air. 

Q.  Why  will  those  vibrations  be  heard  FIRST, 
which  are  made  LAST  ? 

A.  Because  the  flash  (which  produces 
the  sound)  is  almost  instantaneous,  but 
sound  takes  a  whole  second  of  time  to 
travel  380  yards. 

Q.  If  a  thunder-cloud  were  1900  yards  off, 
how  long  would  the  peal  last  ? 

A.  Five  seconds :  we  should^rsZ  hear 
the  vibrations  produced  in  those  portions 
of  the  air  contiguous  to  the  earth ;  then 
those  more  remote ;  and  it  would  be  5 
seconds  before  those  vibrations  reached 
us,  which  were  made  in  the  immediate 
vicinity  of  the  cloud. 

380  X  5  =  1900. 

A  popular  method  of  telling  how  far  the  storm  is  off  is 
fiiis — Immediately  you  see  the  flash,  put  your  hand  upon 
your  pulse,  and  count  how  many  times  it  beats  before  you 
hear  the  thunder:  if  it  beats  6  pulsations,  the  storm  is  1 
mile  off;  if  12  pulsations,  it  is  2  miles  off,  and  so  on. 

Q.  Why  is  the  THUNDER  sometimes  like  a  deep 
GROWL  ? 

A.  Because  the  storm  is  far  distant, 
and  the  sound  of  the  thunder  indistinct. 

Q.  Is  not  the  sound  of  thunder  affected  by 
LOCAL  circumstances  ? 

A.  Yes;  \heflatter  the  country,  the 
more  unbroken  the  peal.  Mountain 


THUNDER-BOLTS.  17 

scenery  breaks  the  peal,  and  makes  it 
harsh  and  irregular. 

Q.       What  is  the  cause  of  ROLLING  THUNDER  ? 

A.  The  vibrations  of  air  (having-  dif- 
ferent lengths  to  travel)  reach  the  ear  at 
successive  intervals. 

The  .reverberation  (or  echo)  amongst  the  massive  clouds 
contributes  in  some  measure  to  this  effect. 

Q.  Why  is  a  flash  of  lightning  generally  fol- 
lowed by  POURING  RAIN  ? 

A.  The  flash  produces  a  change  in 
the  physical  condition  of  the  air,  rendering 
it  unable  to  hold  so  much  water  in  solu- 
tion as  it  could  before ;  in  consequence 
of  which,  a  part  is  given  off  in  heavy 
rain.  ^ 

Q.  Why  is  a  flash  of  lightning  generally  fol- 
lowed by  a  GUST  OF  WIND  ? 

A.  Because  the  physical  condition  of 
the  air  is  disturbed  by  the  passage  of  the 
lightning,  and  •wind  is  the  result  of  this 
disturbance. 

Q.       Why  is  there  NO  THUNDER  to  what  is  called 

SUMMER    LIGHTNING  ? 

A.  Because  the  lightning-clouds  are 
so  far  distant,  that  the  sound  of  the  thun- 
der is  lost,  before  it  reaches  the  ear. 

Q.  Do  THUNDER-BOLTS  ever  drop  from  the 
clouds  ? 

A.     No ;    the  notion  of  thunder-bolts 


18  ELECTRICITY. 

arises,  either  from  the  globular  form 
which  lightning"  sometimes  assumes ;  or 
else  from  the  gaseous  flre-balls,  which 
sometimes  fall  from  the  clouds. 

See  page  13. 
Q.       Why  is  the  THUNDER  often  several  moments 

AFTER    the   FLASH  ? 

A.  Because  it  has  a  long-  way  to 
come.  Lightning-  travels  nearly  a  mil- 
lion times  faster  than  thunder ;  if,  there- 
fore, the  thunder  has  a  long  way  to  come, 
it  will  not  reach  the  earth,  till  a  consi- 
derable time  after  the  flash. 

Q.  Can  we  not  tell  the  DISTANCE  of  a  thunder- 
cloud, by  observing  the  interval  which  elapses  between 
the  flash  and  the  peal  ? 

A.  *Yes  ;  the  flash  is  instantaneous* 
but  thunder  will  take  a  whole  second  of 
time  to  travel  380  yards :  hence,  if  the 
flash  be  5  seconds  before  the  thunder, 
the  cloud  is  1900  yards  off.  (See  note, 
p.  16.) 

i.  e.  380  X  5  =  1900  yards. 

Q.  What  PLACES  are  most  DANGEROUS  during 
a  STORM  ? 

A.  It  is  very  dangerous  to  be  near  a 
tree,  or  lofty  building ;  and  also  to  be 
near  a  river,  or  any  running  water. 

*  The  speed  of  lightning  is  so  great,  that  it  would  go 
480  times  round  the  earth  in  one  minute :  whereas  thun- 
der would  go  scarcely  13  miles  in  the  same  space  of  time. 


LIGHTNING.  19 

Q.  Why  is  it  DANGEROUS  to  be  NEAR  a  TREE, 
or  lofty  building,  during  a  thunder-storm  ? 

A.  Because  a  tall  pointed  object  (like 
a  tree  or  spire)  will  frequently  discharge 
a  lightning-cloud  ;  and  if  any  one  were 
standing  near,  the  lightning  might  di- 
verge from  the  tree,  and  pass  through 
the  fluids  of  the  human  body. 

Q.      How  can  a  TREE  or  SPIRE  DISCHARGE  a 

lightning-cloud  ? 

A.  A  lightning-cloud  (floating  over 
a  plain)  may  be  too  far  off  to  be  dis- 
charged by  it ;  but,  as  a  tree  or  spire 
would  shorten  this  distance,  it  might  no 
longer  be  too  far  off  to  be  discharged. 

For  example.  If  a  lightning-cloud  were  700  yards 
above  the  earth,  it  would  be  too  far  of  to  be  discharged  : 
but  a  tree  or  spire  50  yards  high  would  make  the  cloud 
only  650  yards  off  a  conductor ;  in  consequence  of  which, 
the  cloud  would  be  instantly  discharged. 

Q.      Is  not  AIR  a  CONDUCTOR  of  lightning  ? 

A.  No ;  dry  air  is  not  a  conductor  of 
lightning. 

Q.  Why  would  lightning  fly  from  a  tree  or 
spire,  into  a,  MAN  standing  near  ? 

A.  Because  the  electric  fluid  (called 
lightning)  always  chooses  for  its  path  the 
best  conductors  ;  and,  if  the  human  fluids 
proved  the  better  conductor,  would  pass 
through  the  man  standing  near  the  tree, 
rather  than  down  the  tree  itself. 


20  ELECTRICITY. 

There  would  be  no  danger  if  the  tree  or  spire  were 
made  of  metal ;  because  metal  is  a  better  conductor  than 
the  human  fluids. 

Q.  Does  lightning  go  through  the  inside,  or 
down  the  OUTSIDE  of  a  tree  ? 

A.  It  runs  down  the  outside  of  a  tree ; 
but  passes  through  the  inside  of  a  man. 

Q.  Why  does  lightning  pass  down  the  OUTSIDE 
of  a  tree  ? 

A.  Because  it  always  makes  choice 
of  the  best  conductors ;  and  the  outside 
of  a  tree  is  a  better  conductor  than  the 
inside. 

Q.  Why  does  lightning  pass  through  the  IN- 
SIDE of  a  man  ? 

A.  Because  the  fluids  of  the  human 
body  make  a  better  conductor  than  the 
skin ;  therefore,  lightning*  passes  through 
a  man,  and  not  down  his  skin. 

Q.  Wh,y  is  it  DANGEROUS  to  be  near  a  deep 
RIVER,  or  any  other  running  water,  during  a  thun- 
der-starm  ? 

A.  Because  running  water  is  a  good 
conductor ;  and  lightning  always  takes 
in  its  course  the  best  conductors. 

Q.  Why  is  it  dangerous  for  a  man  to  be  NEAR. 
WATER  in  a  thunder-storm  ? 

A.  Because  the  height  of  a  man  may 
be  sufficient  to  discharge  a  cloud  :  and 
(if  there  were  no  taller  object  nigh)  the 


LIGHTNING.  21 

lightning-  might  make  the  man  its  con- 
ductor to  the  water. 

See  note  on  p.  19. 

Q.  Why  is  it  DANGEROUS  to  RING  CHURCH 
BELLS  during  a  thunder-storm  ? 

A.  For  two  reasons :  1st — Because 
the  steeple  may  discharge  the  lightning- 
cloud,  merely  from  its  lieiglit ;  and 

2dly — As  the  swinging  of  the  bells 
puts  the  air  in  motion,  it  diminishes  its 
resistance  to  the  electric  fluid. 

Q.  Why  is  it  unsafe  to  RUN  or  DRIVE  FAST 
during  a  thunder-storm  ? 

A.N  Because  it  produces  a  current  of 
air ;  and,  as  air  in  motion  affords  less 
resistance  to  the  flash,  it  is  a  better  con- 
ductor than  air  in  a  state  of  rest. 

Q.  What  PARTS  of  a  DWELLING  are  most  DAN- 
GEROUS during  a  thunder-storm  ? 

A.  The  fire-place,  especially  if  the 
fire  be  lighted;  the  attics  and  cellar.  It 
is  also  imprudent  to  sit  close  by  the 
walls,  to  ring  the  bell,  or  to  bar  the  shut- 
ters, during  a  thunder-storm. 

Q.  Why  is  it  DANGEROUS  to  sit  BEFORE  A 
FIRE  during  a  thunder-storm  ? 

A.  Because  the  heated  air  and  soot 
are  conductors  of  lightning ;  especially 
when  connected  with  such  excellent 


22  ELECTRICITY. 

conductors  as  the  stove,  fender  and  fire- 
irons. 

Q.  Why  are  ATTICS  and  CELLARS  more  DAN- 
GEROUS in  a  thunder-storm^  than  the  middle  story 
of  a  house  ? 

A.  Because  lightning*  some  ti  mes  pass- 
es from  the  clouds  to  the  earth,  and  some- 
times from  the  earth  to  the  clouds ;  in 
either  cases  the  middle  story  would  be 
the  safer  place. 

Q.       When   does    lightning    pass    FROM    THE 

EARTH  to  the  CLOUDS  ? 

A.  When  the  clouds  are  in  a  "nega- 
tive77 state  of  electricity. 

Q.       When   does   lightning    pass    FROM    THE 

CLOUDS  to  the  EARTH  ? 

A.  When  the  clouds  are  in  a  "  posi- 
tive" state  of  electricity. 

Q.  What  is  meant  by  the  clouds  being  in  a 
"positive  state  of  electricity?" 

A.  When  the  clouds  contain  more 
electric  fluid  than  they  generally  do,  they 
are  said  to  be  in  a  "positive  state  of  elec- 
tricity." 

Q.  What  is  meant  by  the  clouds  being  in  a 
"  negative  state  of  electricity .?" 

A.  When  the  clouds  contain  less 
electric  fluid  than  they  ought  to  do,  they 
are  said  to  be  in  a  "  negative  state  of 
electricity." 


LIGHTNING.  23 

Q.  Does  the  flash  proceed  from  a  negative  or 
POSITIVE  body  ? 

A.  Always  from  a  positive  body ; 
that  is,  from  one  over-charged  with  elec- 
tric fluid. 

It  is  generally  thought  that  there  are  two  sorts  of  elec- 
tricity, one  called  VITREOUS,  corresponding  to  positive  elec- 
tricity ;  and  the  other  called  RESINOUS,  corresponding  to 
negative  electricity. 

Q.  When  lightning  flashes  from  the  earth  to 
the  clouds,  what  is  the  flash  called  ? 

A.  It  is  popularly  called  the  "return- 
ing1 stroke  ;"  because  the  earth  (being 
over-charged  with  electric  fluid)  returns 
the  surplus  quantity  to  the  clouds. 

Q.  Why  is  it  DANGEROUS  to  lean  AGAINST  A 
WALL  during  a  thunder-storm  ? 

A.  Because  the  electric  fluid  will 
sometimes  run  down  a  wall ;  and  (as  a 
man  is  a  better  conductor  than  a  wall) 
would  leave  the  wall,  and  run  down  the 
man. 

Q.  Why  is  it  dangerous  to  RING  a  BELL  dur- 
ing a  thunder-storm  ? 

A.  Bell- wire  is  an  excellent  conduc- 
tor;  and  (if  a  person  were  to  touch  the 
bell-handle)  the  electric  fluid,  passing 
down  the  wire,  might  run  through  his 
hand  and  injure  it. 

Q.  Why  would  the  lightning  run  through  a 
man  touching  a  bell- handle  ? 


24  ELECTRICITY. 

A.  Because  the  human  body  is  a 
better  conductor  than  the  wall  (between 
the.  bell-handle  and  the  floor) ;  and  as 
lightning*  always  choos63s  the  best  con- 
ductor for  its  path,  it  would  (in  this  case) 
pass  through  the  man,  and  injure  him. 

Q.  Why  is  it  DANGEROUS  'to  BAR  a  SHUTTER 
during  a  thunder -storm  ? 

A.  Because  the  iron  shutter-bar  is  an 
excellent  conductor  ;  and  the  electric  fluid 
might  run  from  the  bar  through  the  per- 
son touching  it,  and  injure  him. 

Q.  Why  is  it  dangerous  to  be  in  a  CROWD 
during  a  thunder-storm? 

A.  For  two  reasons  :  1st — Because 
a  mass  of  people  forms  a  better  conductor 
than  an  individual ;  and 

2dly — Because  the  vapor  arising  from 
a  crowd  increases  its  conducting  power. 

Q.  Why  is  a  MASS  of  bodies  a  better  conductor 
than  a  single  body  ? 

A.  Each  living  body  is  a  conductor 
of  electricity;  and  a  connected  mass  of 
such  conductors  is  more  likely  to  be 
struck,  than  a  single  individual. 

Q.  Why  is  the  danger  increased  by  the  VAPOR 
which  rises  from  a  crowd  ? 

A.  Because  vapor  is  a  conductor , 
and  the  more  conductors  there  are,  the 
greater  the  danger  will  be. 


LIGHTNING.  25 

Q.  Why  is  a  THEATRE  dangerous  during  a 
thunder-storm  ? 

A.  Because  the  crowd,  and  great  va- 
por arising  from  so  many  living  bodies, 
render  it  an  excellent  conductor  of  light- 
ning. 

Q.  Why  is  a  FLOCK  of  sheep  in  greater  dan- 
ger than  a  smaller  number  ? 

A.  1st — Because  each  sheep  is  a  con- 
ductor of  lightning1,  and  the  conducting 
power  of  the  flock  is  increased  by  its 
numbers :  and 

2dly — The  very  vapor  arising  from  a 
flock  of  sheep  increases  its  conducting 
poiver,  and  its  danger. 

Q.  Why  is  a  HERD  of  cattle  in  danger  during 
a  storm  1 

A.  1st — Because  the  number  of  living- 
bodies  increases  the  conducting  power 
of  their  animal  fluids  :  and 

2dly — The  very  vapor  arising  from  a 
herd  increases  its  conducting  power. 

Q.  If  a  person  be  ABROAD  in  a  thunder-storm, 
what  place  is  the  SAFEST  ? 

A.  Any  place  about  20  or  30  feet 
from  some  tall  tree  or  building ;  except 
it  be  near  to  running  water. 

Q.  Wh.y  would  it  be  safe  to  stand  20  or  30 
feet  from  some  tall  tree,  in  a  thunder-storm  ? 

A.     Because  the  lightning  would  al- 
2 


26  ELECTRICITY. 

ways  choose  the  tall  tree  as  a  conductor ; 
and  we  should  riot  be  sufficiently  near 
the  tree,  for  the  lightning  to  diverge  from 
it  to  us. 

Q.  If  a  person  be  in  A  CARRIAGE  in  a  thun- 
der-storm, in  what  way  can  he  travel  most  SAFELY  ? 

A.  He  should  not  lean  against  the 
carriage  ;  but  sit  upright,  without  touch- 
ing any  of  the  four  sides. 

Q.  Why  should  not  a  person  lean  AGAINST  the 
carriage  in  a  storm  ? 

A.  Because  the  electric  fluid  might 
run  down  the  sides  of  the  carriage  ;  and 
(if  a  person  were  leaning  against  them) 
would  make  choice  of  him  for  a  conduct- 
or, and  perhaps  destroy  life. 

Q.  If  a  person  be  in  A  HOUSE  during  a  thun- 
der-storm,  what  place  is  SAFEST  ? 

A.  Any  room  in  the  middle  story. 
The  middle  of  the  room  is  best ;  espe- 
cially if  you  place  yourself  on  a  mat- 
tress, bed,  or  hearth-rug. 

Q.  Why  is  the  MIDDLE  STORY  of  a  house  SAF- 
EST in  a  thunder-storm  ? 

A.  Because  the  fluid  (if  it  struck  the 
house  at  all)  would  be  diffused  among 
the  several  conductors  of  the  upper  part 
of  the  house,  before  it  reached  the  midr 
dle  story ;  in  consequence  of  which,  its 
force  would  be  weakened. 


LIGHTNING.  27 

Q.  Why  is  the  MIDDLE  of  the  ROOM  more  SAFE 
than  any  other  part  of  it,  in  a  thunder-storm  ? 

A.  Because  the  lightning1  (if  it  struck 
the  room  at  all)  would  come  down  the 
chimney,  or  walls  of  the  room  ;  and, 
therefore,  the  further  distant  from  these, 
the  better. 

Q.  Why  is  a  MATTRESS,  BED,  or  HEARTH-RUG 
a  good  security  against  injury  from  lightning? 

A.  Because  they  are  all  non-conduct- 
ors ;  and,  as  lightning*  always  makes 
choice  of  the  best  conductors,  it  would 
not  choose  for  its  path  such  things  as 
these. 

Q.  Is  it  better  to  be  WET  or  dry  during  a 
storm  ? 

A.  To  be  wet :  if  a  person  be  in  the 
open  field,  the  best  thing  he  can  do,  is 
to  stand  about  20  feet  from  some  tree, 
and  get  completely  drenched  to  the  skin. 

Q.       Why  is  it  better  to  be  WET  than  dry  ? 

A.  Because  wet  clothes  form  a  better 
conductor  than  the  fluids  of  our  body  ; 
and,  therefore,  lightning  would  pass 
down  our  wet  clothes,  without  touching 
our  body  at  all. 

Q.  What  is  the  SAFEST  thing  a  person  can  do^ 
to  avoid  injury  from  lightning? 

A.  He  should  draw  his  bedstead 
into  the  middle  of  the  room,  commit 


28  ELECTRICITY. 

himself  to  the  care  of  God,  and  g*o  to 
bed  ;  remembering1  that  our  Lord  has 
said,  "  The  very  hairs  of  your  head  are 
all  numbered." 

N.  B.  No  great  danger  needs  really  to  be  apprehended 
from  lightning,  if  you  avoid  taking-  your  position  near  tall 
trees,  spires,  or  other  elevated  objects. 

Q.      What  is  a  LIGHTNING-CONDUCTOR  ? 

A.  A  metal  rod  fixed  in  the  earth, 
running-  up  the  whole  height  of  a  build- 
ing1, and  rising1  in  a  point  above  it. 

Q.       What  metal  is  the  best  for  this  purpose  ? 

A.     Copper  makes  the  best  conductor. 

Q.       Why  is  COPPER  belter  than  iron  ? 

A.  1st — Because  copper  is  a  better 
conductor  than  iron : 

2dly — It  is  not  so  easily  fused  or 
melted:  and 

3dly — It  is  not  so  much  injured  by 
weather. 

Q.       What  is  the  USE  of  a  lightning-conductor  ? 

A.  As  metal  is  a  most  excellent  con- 
ductor, lightning1  (which  makes  choice 
of  the  best  conductors)  will  run  down  a 
metal  rod,  rather  than  the  walls  of  the 
building. 

Q.  How  FAR  will  the  beneficial  influence  of  a 
lightning-conductor  extend  ? 

A.     It  will  protect  a  space  all  round, 


LIGHTNING.  ffd 

4  times  the  length  of  that  part  of  the  rod 
which  rises  above  the  building. 

Q.       Give  me  an  example. 

A.  If  the  rod  rise  2  feet  above  the 
house,  it  will  protect  the  building  for  (at 
least)  8  feet  all  round. 

Q.  Why  are  not  lightning-conductors  more 
generally  used  ? 

A.  Because  many  accidents  have 
arisen  from  conductors  of  defective  con- 
struction. 

Q.  How  can  lightning-conductors  be  produc- 
tive of  HARM  ? 

A.  If  the  rod  be  broken  by  weather 
or  accident,  the  electric  fluid  (being 
obstructed  in  its  path)  will  damage  the 
building. 

Q.  Is  there  any  other  evil  to  be  apprehended 
from  a  lightning-rod  ? 

A.  Yes  ;  if  the  rod  be  not  big  enough 
to  conduct  the  whole  current  to  the  earth, 
the  lightning  will  fuse  the  metal,  and 
injure  the  building. 

The  conducting  rod  should  be  (at  least)  one  inch  in  di- 
ameter. 

Q.  How  does  LIGHTNING  sometimes  KNOCK 
DOWN  HOUSES  and  churches  ? 

A.  The  steeple  or  chimney  is  first 
struck ;  the  lightning  then*  darts  to  the 
iron  bars  and  cramps,  employed  in  the 


30  ELECTRICITY. 

building ;  and  (as  it  darts  from  bar  to 
bar)  shatters  to  atoms  the  bricks  and 
stones  which  oppose  its  progress. 

Q.  Can  you  tell  me  how  St.  Bride's  Church 
(London)  was  nearly  destroyed  by  lightning ,  about 
100  years  ago  ? 

A.  The  lightning  first  struck  the 
metal  vane,  and  ran  down  the  rod  ;  it 
then  darted  to  the  iron  cramps,  employed 
to  support  the  building ;  and  (as  it  flew 
from  bar  to  bar)  smashed  the  stones  of 
the  church  which  lay  between.  . 

Q.  Why  did  the  Lightning  fly  about  from 
place  to  place,  and  not  pass  down  in  a  straight 
course  ? 

A.  Because  it  always  takes  in  its 
course  the  best  conductors ;  and  will  fly 
both  right  and  left,  in  order  to  reach 
them. 

Q.       Why  does  LIGHTNING  turn  milk  SOUR  ? 

A.  Lightning  causes  the  gases  of  the 
air  (through  which  it  passes)  to  combine, 
and  thus  produces  a  poison,  called  nitric 
acid  ;  some  small  portion  of  which,  mix- 
ing with  the  milk,  turns  it  sour.* 

>  *  The  air  is  composed  of  two  gases,  called  oxygen  and 
nitrogen,  mixed  together,  but  not  combined.  Oxygen  com- 
bined with  nitrogen,  produces  five  deadly  poisons,  viz. — 
nitrous  oxide,  nitric  oxide,  hyponitrous  acid,  nitrous  acid, 
and  nitric  acid,  according  to  the  proportion  of  each  gas  in 
the  combination. 


LIGHTNING.  31 

N.  B.    Sometimes  the  mere  heat  of  the  air,  during  the 
btorm,  turns  milk  sour. 

Q.  What  is  the  difference,  "between  COMBINING 
and  MIXING  ? 

A.  When  different  ingredients  are 
mingled  together  without  undergoing  any 
chemical  change,  they  are  said  to  be 
mixed  ;  but  when  the  natural  properties 
of  each  are  altered  by  the  union,  then  those 
ingredients  are  said  to  be  combined. 

Q.       Give  me  an  example. 

A.  Different  colored  sands  (shaken  to- 
gether in  a  bottle)  will  mix  together,  but 
not  combine:  but  water  poured  on  quick- 
lime, will  combine  with  the  lime,  and  not 
mix  with  it. 

Q.  Why  are  different  grains  of  sand  said  to 
be  MIXED,  when  they  are  shaken  together  ? 

A.  Because  (though  mingled  togeth- 
er) the  property  of  each  grain  remains 
the  same  as  it  was  before. 

Q.  Why  is  water  ^  poured  on  lime,  said  to 
COMBINE  with  it  ? 

A.  Because  the  properties  of  each 
are  altered  by  the  mixture  ;  the  lime  al- 
ters the  character  of  the  water,  and  the 
water  that  of  the  lime. 

Q.  Do  oxygen  and  nitrogen  COMBINE,  or  only 
MIX  together,  in  common  atmospheric  air  ? 

A.     They  only  mix  together,  as  grains 


32  ELECTRICITY. 

of  sand  would  do  when  shaken  in  a  bot- 
tle. When  oxygen  arid  nitrogen  com- 
bine, they  do  not  constitute  air,  but  acid 
poisons.  (See  note  on  p.  30.)  . 

Q.  Why  does  LIGHTNING  turn  BEER  SOUR,  al- 
though contained  in  a  close  cask  ? 

A.  Because,  if  beer  be  new  and  the 
process  of  fermentation  incomplete,  light- 
ning will  so  accelerate  the  process,  as  to 
turn  the  sugar  into  acetic  acid  at  once, 
without  passing  through  the  interme- 
diate state  of  alcohol. 

Q.  Why  is  NOT  OLD  beer  and  strong  PORTER 
made  SOUR  by  lightning  ? 

A.  Because  the  fermentation  is  more 
complete  ;  and,  therefore,  is  less  affected 
by  electrical  influence. 

Q.  Why  is  METAL  sometimes  FUSED  by  light' 
ning  ? 

A.  Because  the  dimension  of  the 
metal  is  too  small  to  afford  a  path  for  the 
electric  current. 

Q.       Why  does  LIGHTNING  PURIFY  the  AIR  ? 

A.  For  two  reasons :  1st — Because 
the  electric  fluid  produces  "  nitric  acid" 
in  its  passage  through  the  air : 

2dly — Because  the  agitation  of  the 
storm  stirs  up  tfie  air. 


LIGHTNING.  33 

The  "  nitric  acid"  is  produced  by  the  combination  of 
some  portions  of  the  oxygen  and  nitrogen  of  the  air.* 

Q.  How  does  the  production  of  nitric  acid  PURI- 
FY the  air  ? 

A.  Nitric  acid  acts  very  powerfully 
in  destroying  the  exhalations,  which  arise 
from  putrid  vegetable  and  animal  matters. 

Q.  Why  is  LIGHTNING  more  common  in  SUM- 
MER and  in  AUTUMN,  than  in  spring  and  winter  ? 

A.  Because  the  heat  of  summer  and 
autumn  produces  great  evaporation ;  and 
the  conversion  of  water  into  vapor  always 
developes  electricity. 

Q.  Why  does  a  THUNDER-STORM  generally  fol- 
low very  dry  weather  ? 

A.  Because  dry  air  (being-  a  non- 
conductor) will  not  relieve  the  clouds  of 
their  electricity ;  so  the  fluid  accumulates, 
till  the  clouds  are  discharged  in  a  storm. 

Q.  Why  does  a  THUNDER-STORM  rarely  suc- 
ceed WET  weather  ? 

A.  Because  moist  air  or  falling  rain 
(being  a  conductor)  carries  down  the 
electric  fluid  gradually  and  silently  to 
the  earth. 

Q.  What  is  the  general  DIRECTION  of  a  THUN- 
DER-STORM ? 


*  The  oxygen  and  nitrogen  are  not  combined,  but  simply 
mixed,  in  the  ordinary  air;   but  lightning  causes  some 
portions  of  the  mixed  elements  to  combine.  See  note,  p.  30. 
2* 


34  ELECTRICITY. 

A.  Either  from  east  to  west ;  or  from 
north  to  south. 

Q.      Why  is  ELECTRICITY  excited  by  FRICTION  ? 

A.  Electricity,  like  heat,  exists  in  all 
matter ;  but  is  often  in  a  latent  state  : 
friction  disturbs  it,  and  brings  it  into 
active  operation. 

"  Latent,"  see  p.  37. 

Q.  Why  is  a  TREE  sometimes  SCORCHED  by 
lightning,  as  if  it  had  been  set  on  fire  ? 

A.  Lightning  scorches  by  its  own 
positive  heat,  just  the  same  as  fire  would. 

Q.  Why  is  the  BARK  of  a  TREE  often  ripped 
quite  off  by  a  flash  of  lightning  ? 

A.  Because  the  latent  heat  of  the 
tree  (being  very  rapidly  developed  by 
the  electric  fluid)  forces  away  the  bark 
in  its  impetuosity  to  escape. 

Some  part  of  this  is  probably  due  to  the  simple  mechan- 
•  ical  force  of  the  lightning. 

Q.  Why  are  BOUGHS  of  TREES  broken  off  by 
lightning  ? 

A.  Because  the  mechanical  force  of 
lightning  is  very  great;  and,  as  the 
boughs  of  a  tree  are  imperfect  conduct- 
ors, they  will  often  be  broken  off  by  this 
force. 

Q.       Why  is  an  electric  shock  felt  MOST  at  the 

\ ELBOW   JOINT? 

A.     Because  the  path  of  the  fluid  is 


LIGHTNING.  35 

obstructed  by  the  joint ;  and  the  shock 
(felt  at  the  elbow)  is  caused  by  the  fluid 
leaping  from  one  bone  to  another. 

Q.       Is  electricity  accompanied  with  any  ODOR  1 

A.  Yes  ;  near  a  large  electrical  ma- 
chine in  good  action,  there  is  always  a 
peculiar  odor,  resembling*  sulphur  and 
2)Iiosphorus  ;  this  odor  is  called  -"  OZONE." 

Pronounce  O-ZONE,  in  two  syllables. 

Q.  Has  this  peculiar  odor,  called  "  OZONE," 
"been  observed  in  thunder-storms  ? 

A.  Yes ;  sometimes  the  sulphurous 
odor  prevails,  and  sometimes  the  phos- 
phoric. 

If  the  gaseous  body  disengaged  by  lightning,  reaches  us 
in  a  concentrated  form,  the  odor  is  SULPHUROUS  ;  if  in  a 
diluted  form,  it  is  PHOSPHORIC. 

Q.       What  are  FUL'GURITES  ? 
A.     Hollow  tubes  produced  in  sandy 
soils  by  the  action  of  lightning1. 

Q.       How  does  lightning  produce  fulgurites  ? 

A.  When  it  enters  the  earth,  it  fuses 
the  flinty  matter  of  the  soil  into  a  vitre- 
ous (or  glassy)  substance,  called  a  ful- 
gurite. 

Q.  Does  not  lightning  sometimes  affect  the 
character  of  IRON  and  STEEL  ? 

A.  Yes ;  bars  of  iron  and  steel  are 
sometimes  rendered  magnetic  by  light- 
ning. 


36  CHEMICAL    ACTION. 

Q.  Give  me  an  instance  of  the  magnetic  effects 
of  lightning. 

A.  Sometimes  it  will  reverse  the  mag- 
netic needles  of  the  electric  telegraph, 
and  sometimes  destroy  their  magnetism 
altogether. 

Q.  What  is  meant  by  the  magnetic  needles 
being  REVERSED  ? 

A.  That  part  of  the  needle  which 
ought  to  point  toward  the  nortk,  is  made 
to  point  toward  the  south  ;  and  that  part 
which  ought  to  point  south,  is  made  to 
point  toward  the  north. 

Q.  How  does  lightning  act  upcm  the  magnetic 
needles  of  the  electric  telegraph  ? 

A.  The  electric  fluid  is  conveyed 
along  the  conducting  wires  to  the  tele- 
graphic needles. 


CHEMICAL    ACTION. 
CHAPTER   III. 

Q.       What  is  the  THIRD  chief  source  of  heat  ? 

A.     CHEMICAL  ACTION. 

Q.       What  is  meant  by  chemical  action  being 
the  source  of  heat  ? 

A.     Many  things,  when  their  chemical 
constitution  is  changed  (either  by  the 


LATENT    HEAT.  37 

abstraction  of  some  of  their-  gases,  or  by 
the  combination  of  others  not  before  unit- 
ed) evolve  heat,  while  the  change  is  go- 
ing on. 

Q.       Explain  by  illustration  what  you  mean. 

A.  Water  is  cold,  and  sulphuric  acid 
is  cold ;  but  if  these  two  cold  liquids  be 
mixed  together,  they  will  produce  intense 
heat. 

Q.  Why  does  COLD  WATER,  poured  on  LIME, 
make  it  intensely  HOT  ? 

A.  Because  heat  is  evolved  by  the 
chemical  action  which  takes  place,  when 
the  cold  water  combines  with  the  lime. 

N.  B.  Heat  is  always  evolved,  when  a  fluid  is  converted 
into  a  solid  form.  Heat  is  always  absorbed^  when  a  solid  is 
changed  into  a  liquid  state.  As  the  water  is  changed  from 
its  liquid  form  when  it  is  taken  up  by  the  lime,  therefore, 
heat  is  given  off.  « 

Q.       Where  does  the  heat  come  from  ? 

A.  It  was  in  the  water  and  lime  be- 
fore ;  but  was  in  a  latent  state. 

Q.  Was  there  heat  in  the  cold  water  and  lime^ 
before  they  were  mixed  together  ? 

A.  Yes.  All  bodies  contain  heat; 
the  coldest  ice,  as  well  as  the  hottest  fire. 

Q.       Is  there  HEAT  even  in  ICE  ? 

A.  Yes ;  but  it  is  latent  (i.  e.,  not  per- 
ceptible to  our  senses.) 

Latert,  from  the  Latin  word  Lateo,  (to  lie  hid.) 


38  CHEMICAL    ACTION. 

Q.  How  do  you  KNOW  there  is  heat,  if  you 
cannot  PERCEIVE  it  ? 

A.  Thus:— Ice  is  32°  by  the  ther- 
mometer ;  but  if  ice  be  melted  over  a  fire, 
(though  140°  of  heat  are  absorbed  by  the 
process,)  it  will  feel  no  hotter  than  before. 

i.  e.,  it  will  be  only  32°,  and  not  172°.* 
Q.       What  becomes  of  the  140°  which  went  into 
the  ice  to  melt  it  ? 

A.  It  is  hidden  in  the  water  ;  or  (to 
speak  more  scientifically)  it  is  stored  up 
in  a  latent  state. 

Q.  How  MUCH  heat  may  be  thus  secreted  or 
made  latent  ? 

A.  All  things  contain  a  vast  quantity 
of  latent  heat ;  but  as  much  as  1140°  of 
heat  may  remain  latent  in  water. 

Q.  How  can  1 140°  of  heat  be  added  to  water, 
without  bein^  perceptible  to  our  feelings? 

A.  1st — 140°  of  heat  are  hidden  in 
water,  when  ice  is  melted  by  the  sun  or 
fire. 

2dly — -1000°  more  of  heat  are  secret- 
ed, when  water  is  converted  into  steam. 
Thus,  before  ice  is  converted  into  steam, 
1140°  of  heat  become  latent. 

One  pint  of  boiling  water,  (212°  according  to  the  ther- 
mometer,) will  make  1800  pints  of  steam;  but  the  steam 
is  no  hotter  to  the  touch  than  boiling  water — both  are 
212° ;  therefore,  when  water  is  converted  into  steam,  1000° 

*  32°,  i.  e.,  32  degrees ;  140°,  i.  e.,  140  degrees,  &c. 


COMBUSTION.  39 

of  heat  become  latent.    Hence,  before  ice  is  converted 
into  steam,  it  must  contain  1140°  of  latent  heat. 

Q.  Can  we  be  made  to  FEEL  the  heat  of  ICE  or 
snow  ? 

A.  Yes.  Into  a  pint  of  snow  put  half 
as  much  salt ;  then  plunge  your  hands 
into  the  liquid ;  and  it  will  feel  so  in- 
tensely cold,  that  the  snow  itself  will 
seem  warm  in  comparison  to  it. 

Q.  Is  SALT  and  SNOW  really  COLDER  than 
snow  ? 

A.  Yes,  many  degrees ;  and  by  dip- 
ping your  hand  into  the  mixture  first, 
and  into  snow  afterward,  the  snow  will 
seem  to  be  comparatively  warm. 


CHAPTER  IV.  . 

COMBUSTION. 

Q.       What  is  FIRE? 

A.  Heat  and  light,  produced  by  the 
combustion  of  inflammable  substances. 

Q.      How  is  HEAT  evolved  by  combustion? 

A.  By  chemical  action.  As  latent  heat 
is  liberated,  when  water  is  poured  upon 
lime,  by  chemical  action  ;  so  latent  heat 
is  liberated  in  combustion,  by  chemical 
action  also. 


40  CHEMICAL    ACTION. 

Q.  What  CHEMICAL  ACTION  takes  place  in 
combustion? 

A.     The  elements  of  the  fuel  combine 

with  the  oxygen  of  the  air. 

Q.       What  is  meant  by  the  "ELEMENTS  OF  FUEL?'' 
A.     As  bread  is  a  compound  of  flour7 

yeast,  and  salt ;  so  fuel  is  a  compound 

of  hydrogen  and  carbon. 

Q.       What  are  the  ELEMENTS  of  atmospheric  AIR? 

A.  Oxygen  and  nitrogen,  mixed  toge- 
ther in  the  following  proportions ;  4 
gallons  of  nitrogen  and  one  of  oxygen 
will  make  5  gallons  of  common  air. 

Q.      What  is  CARBON? 

A.  The  solid  part  of  fuel.  Carbon 
abounds  in  all  animal  bodies,  earths,  and 
even  in  some  minerals. 

Q.      Mention  some  different  species  of  CARBON. 

A.  Common  charcoal,  lamp-black^ 
coke,  and  the  diamond. 

Q.       What  is  HYDROGEN  ? 

A.  An  inflammable  gas.  The  gas 
used  in  our  streets  is  hydrogen  driven 
out  of  coals  by  heat. 

Coal  gas  (more  correctly  speaking)  is  carburetted  hy- 
drogen, i.  e.,  carbon  and  hydrogen.    See  p.  262. 

Q.  What  are  the  peculiar  characteristics  of 
hydrogen  gas? 

A.  1st — It  is  the  lightest  of  all  known 
substances : 


COMBUSTION.  41 

2dly — It  will  burn  immediately  it  is 
ignited:  and 

3dly — A  lighted  candle  (immersed  in 
this  gas)  will  be  instantly  extinguished.* 

Q.       What  is  OXYGEN  ? 

A.  A  gas,  much  heavier  than  hydro- 
gen ;  it  gives  brilliancy  to  flame,  and  is 
essential  to  animal  life.t 

*  Hydrogen  gas  may  be  made  thus : — Put  some  pieces 
of  zinc  or  iron  filings  into  a  glass :  pour  over  them  a  little 
sulphuric  acid  (vitriol),  diluted  with  twice  the  quantity 
of  water ;  then  cover  the  glass  over  for  a  few  minutes, 
and  hydrogen  gas  will  be  given  off. 

EXPERIMENTS. 

If  a  flame  be  put  into  the  glass,  an  EXPLOSION  will  be 
made. 

If  the  experiment  be  tried  in  a  phial,  which  has  a  piece 
of  tobacco-pipe  run  through  the  cork,  and  a  light  held  a 
few  moments  to  the  top  of  a  pipe,  a  FLAME  will  be  made. 

If  a  balloon  be  held  over  the  phial,  (so  that  the  gas  can 
inflate  it,)  the  balloon  will  ascend  in  a  very  few  minutes. 

f  Oxygen  gas  is  much  more  troublesome  to  make  than 
hydrogen.  The  cheapest  plan  is  to  put  a  few  ounces  of 
manganese  (called  the  black  oxide  of  manganese)  into  an 
iron  bottle,  furnished  with  a  bent  tube ;  set  the  bottle  on 
a  fire  till  it  becomes  red  hot,  and  put  the  end  of  the  tube 
into  a  pan  of  water.  In  a  few  minutes,  bubbles  will  rise 
through  the  water ;  these  bubbles  are  oxygen  gas. 

These  bubbles  may  be  collected  thus : — Fill  a  common 
bottle  with  water ;  hold  it  inverted  over  the  bubbles  which 
rise  through  the  pan,  but  be  sure  the  mouth  of  the  bottle 
be  held  in  the  water.  As  the  bubbles  rise  into  the  bottle, 
the  water  will  run  out ;  and  when  all  the  water  has  run 
out,  the  bottle  is  full  of  gas.  Cork  the  bottle  while  the 
mouth  remains  under  water ;  set  the  bottle  on  its  base ; 
cover  the  cork  with  lard  or  wax,  and  the  gas  will  keep 
till  it  be  wanted. 

N.  B.  The  quickest  way  of  making  oxygen  gas,  is  to 
rub  together  in  a  mortar  half  an  ounce  of  oxide  of  copper, 


42  CHEMICAL    ACTION. 

Q.       What  is  NITROGEN  ? 

A.  An  invisible  gas,  which  abounds 
in  animal  and  vegetable  substances.  The 
following  are  its  peculiar  characteristics : 

1.  It  will  not  burn  ; 

2.  An  animal  cannot  live  in  it ; 

3.  It  is   the    principal   ingredient   in 
common  air.% 

Nearly  4  gallons  out  of  every  5  being  nitrogen  gas. 


and  half  an  ounce  of  chlorate  of  potassa.  Put  the  mix- 
ture into  a  common  oil  flask,  furnished  with  a  cork  which 
has  a  bent  tube  'thrust  through  it.  Heat  the  bottom  of 
the  flask  over  a  candle  or  lamp ;  and  when  the  mixture  is 
red  hot,  oxygen  gas  will  be  given  off.  Note — the  tube 
must  be  immersed  in  a  pan  of  water,  and  the  gas  collected 
as  before. 

(Chloride  of  potassa  may  be  bought  at  any  chemist's ; 
and  oxide  of  copper  may  be  procured  by  heating  a  sheet 
of  copper  red  hot,  and  when  cool,  striking  it  with  a  ham- 
mer ;  the  scales  that  peel  off,  are  oxide  of  copper.) 

EXP.  Put  a  piece  of  red  hot  charcoal  (fixed  to  a  bit  of 
wire)  into  your  bottle  of  oxygen  gas ;  and  it  will  throw 
out  most  dazzling  sparks  of  light. 

Blow  a  candle  out ;  and  while  the  wick  is  still  red,  hold 
the  candle  (by  a  piece  of  wire)  in  the  bottle  of  oxygen 
gas ;  the  wick  will  instantly  ignite,  and  burn  brilliantly. 

(Burning  sulphur  emits  a  blue  flame,  when  immersed 
in  oxygen  gas.) 

*  Nitrogen  gas  may  easily  be  obtained  thus : — Put  a 
piece  of  burning  phosphorus  on  a  little  stand,  in  a  plate 
of  water ;  and  cover  a  bell  glass  over  it.  (Be  sure  the 
edge  of  the  glass  stands  in  the  water.)  In  a  few  minutes 
the  oxygen  of  the  air  will  be  taken  up  by  the  burning 
phosphorus ;  and  nitrogen  alone  will  be  left  in  the  bell 
glass. 

(N.  B.  The  white  fume,  which  will  arise  and  be  absorbed 
by  the  water  in  this  experiment,  is  phosphoric  acid ;  i.  e., 
phosphorus  combined  with  oxygen  of  the  air.) 


COMBUSTION.  43 

Q.       Why  is  there  so  MUCH  nitrogen  in  the  air  ? 

A.  In  order  to  dilute  the  oxygen. 
[f  the  oxygen  were  not  thus  diluted, 
[ires  would  burn  out  too  quickly,  and 
life  would  be  too  rapidly  exhausted. 

Q.  What  three  elements  are  necessary  to  pro- 
duce COMBUSTION  ? 

A.  Hydrogen  gas,  carbon,  and  oxygen 
gas  :  The  two  former  in  the  fuel;  and  the 
last  in  the  air,  which  surrounds  the  fuel. 

Q.       What  causes  the  combustion  of  the  fuel  % 

A.  The  hydrogen  gas  of  the  fuel 
'being  set  free,  and  excited  by  a  match), 
unites  with  the  oxygen  of  the  air,  and 
makes  a  yellow  flame ;  this  flame  heats 
the  carbon  of  the  fuel,  which  (also  uniting 
with  oxygen  of  the  air)  produces  car- 
bonic acid  gas. 

Q.       What  is  CARBONIC  ACID  GAS? 

A.  -Only  carbon  (or  charcoal)  com- 
bined with  oxygen  gas. 

Q.       Why  does  FIRE  produce  HEAT? 

A.  Because  it  liberates  latent  heat 
from  the  air  and  fuel. 

Q.  What  CHEMICAL  CHANGES  in  air  and  fuel 
are  produced  by  COMBUSTION  ? 

A.  1st — Some  of  the  oxygen  of  the 
air,  combining  with  the  hydrogen  of  the 
fuel,  condenses  into  water  :  and 


44  CHEMICAL    ACTION. 

2dly — Some  of  the  oxygen  of  the  air, 
combining*  with  the  carbon  of  the  fuel, 
forms  carbonic  acid  gas. 

Q.  Why  is  a  FIRE  (after  it  has  been  long 
burning)  RED  HOT  ? 

A.  Because  the  whole  surface  of  the 
coals  is  so  thoroughly  heated,  that  every 
part  of  it  is  undergoing  a  rapid  union 
with  the  oxygen  of  the  air. 

Q.  In  a  BLAZING  fire,  why  is  the  TIPPER  sur- 
face of  the  COALS  BLACK,  and  the  LOWER  surface  RED  ? 

A.  Because  carbon  (being  solid)  re- 
quires a  great  degree  of  heat  to  make  it 
unite  with  the  oxygen  of  the  air.  In 
consequence  of  which,  the  hot  under 
surface  of  coals  is  frequently  red  from  its 
union  with  oxygen,  while  the  cold  upper 
surface  remains  black. 

Q.  Which  burns  the  more  quickly ,  a  BLAZING 
fire,  or  a  RED  HOT  one  ? 

A.  Fuel  burns  quickest  in  a  blazing 
fire. 

Q.  Why  do  BLAZING  COALS  BURN  QUICKER 
than  red  hot  ones  ? 

A.  Because  the  inflammable  gases  of 
the  fuel  (which  are  then  escaping)  great- 
ly assist  the  process  of  combustion. 

Q.  Why  do  the  coals  of  a  CLEAR  BRIGHT  fire 
burn  out  more  slowly  than  blazing  coals  ? 

A.     Because  most  of  the  inflammable 


COMBUSTION.  45 

gases,  and  much  of  the  solid  fuel,  have 
been  consumed  already ;  so  that  there 
is  less  food  for  combustion. 

Q.       What  is  SMOKE  ? 

A.  Unconsumed  parts  of  fuel  (prin- 
cipally carbon)  separated  from  the  solid 
mass,  and  carried  up  the  chimney  by 
currents  of  hot  air. 

Q.  Why  is  there  MORE  SMOKE  when  COALS  are 
FRESH  added,  than  when  they  are  red  hot  ? 

A.  Because  carbon  (being-  solid)  re- 
quires a  great  degree  of  heat  to  make  it 
unite  with  oxygen,  (or,  in  other  words,  to 
bring  it  into  a  stateof  perfect  combustion:) 
when  coals  are  fresh  laid  on,  more  carbon 
is  separated  than  can  be  reduced  to  com- 
bustion, and  the  surplus  flies  off  in  smoke. 

Q.       Why  is  there  so  LITTLE  SMOKE  with  a  RED 

HOT  FIRE? 

A.  Because  the  entire  surface  of  the 
coals  is  in  a  state  of  combustion ;  and,  as 
very  little  carbon  remains  unconsumed, 
there  is  but  little  smoke. 

Q.  Why  are  there  DARK  and  BRIGHT  SPOTS  in 
a  CLEAR  cinder  FIRE  ? 

A.  Because  the  intensity  of  the  com- 
bustion is  greater  in  some  parts  of  the 
fire,  than  it  is  in  others. 

Q.  Why  is  the  intensity  of  the  combustion  so 
UNEQUAL  ? 


46  CHEMICAL    ACTION. 

A.  Because  the  air  flies  to  the  fire  in 
various  and  unequal  currents. 

Q.  Why  do  we  see  all  sorts  of  GROTESQUE 
FIGURES  in  hot  COALS  ? 

A.  Because  the  intensity  of  combus- 
tion is  unequal^  (owing"  to  the  gusty 
manner  in  which  the  air  flies  to  the  fuel :) 
and  the  various  shades  of  red,  yellow, 
and  white  heat  (mingling  with  the  black 
of  the  unburnt  coal),  produce  strange 
and  fanciful  resemblances. 

Q.  Why  does  PAPER  BURN  more  readily  than 
wood  ? 

A.  Because  it  is  of  a  more  fragile 
texture;  and,  therefore,  its  component 
parts  are  more  easily  heated. 

Q.  Why  does  WOOD  BURN  more  readily  than 
coal  ? 

A.  Because  it  is  not  so  solid ;  and, 
therefore,  its  elemental  parts  are  more 
easily  separated,  and  made  hot. 

Q.  When  a  FIRE  is  LIGHTED,  why  is  PAPER 
laid  at  the  BOTTOM,  against  the  grate  ? 

A.  Because  paper  (in  consequence 
of  its  fragile  texture)  very  readily  catches 
fire. 

Q.       Why  is  WOOD  laid  on  the  top  of  the  paper  ? 
A.     Because  wood  (being  more  sub- 
stantial") burns  longer  than  paper ;  and, 


COMBUSTION.  47 

therefore,   affords   a   longer  contact  of 
flame  to  heat  the  coals. 

Q.       Why  would  not  paper  do  WITHOUT  wood  ? 

A.  Because  paper  burns  out  so  rap- 
idly, that  it  would  not  afford  sufficient 
contact  of  flame  to  heat  the  coals  to  com- 
bustion. 

Q.  Why  will  'not  wood  do  WITHOUT  shavings, 
straw,  or  paper  ? 

A.  Because  wood  is  too  substantial 
to  be  heated  into  combustion  by  the  fee- 
ble flame  issuing-  from  a  match. 

Q.  Why  would  not  the  paper  do  as  welL  if 
placed  on  the  TOP  of  the  coals  ? 

A.     Because  every  blaze   tends  up- 

ward;    if,   therefore,   the    paper   were 

placed  on  the  top  of  the  coals  its  blaze 

'  would  afford  no  contact  of  flame  to  the 

fuel  lying*  below. 

Q.       Why  should  COAL  be  placed  ABOVE  the  wood  ? 

A.  Because  otherwise,  the  flame  of 
the  fuel  would  not  rise  through  the  coal, 
to  heat  it. 

Q.  Why  is  a  FIRE  KINDLED  at  the  LOWEST 
BAR  of  a  grate? 

A.  That  the  flame  may  ascend 
through  the  fuel,  to  heat  it.  If  the  fire 
were  kindled  from  the  top,  the  flame 
would  not  come  in  contact  with  the  fuel 
placed  below. 


48  CHEMICAL    ACTION. 

Q.  Why  does  COAL  make  such  EXCELLENT 
FUEL  ? 

A.  Because  it  contains  a  large 
amount  of  carbon  and  hydrogen  gas,  in  a 
very  compact  and  convenient  form. 

Q.  Why  will  CINDERS  become  RED  HOT  more 
quickly  than  COALS  1 

A.  Because  they  are  sooner  reduced 
to  a  state  of  combustion,  as  they  are 
more  porous  and  less  solid. 

Q.       Why  will  not  IRON  CINDERS  burn  ? 

A.  Because  they  contain  impurities, 
which  are  not  so  ready  to  combine  with 
oxygen,  as  carbon  and  hydrogen  are. 

Q.       Why  are  CINDERS  lighter  than  COALS  ? 

A.     Because   they  are   full   of  little 
holes ;    from   which   vapor,  gases,  and 
other  volatile  parts,  have  been  driven  ] 
off  by  previous  combustion. 

Q.  Why  will  not  STONES  do  for  fuel  as  well  as 
COALS  ? 

A.  Because  they  contain  no  hydrogen, 
and  little  or  no  carbon. 

Q.       Why  will  not  WET  KINDLING  light  afire  ? 

A.  1st — Because  the  moisture  of  the 
wet  kindling  prevents  the  oxygen  of  the 
air  from  getting  to  the  fuel ;  and 

2dly— The  heat  of  the  fire  is  perpetu- 
ally drawn  off,  by  the  conversion  of  water 
into  steam. 


COMBUSTION.  49 

Q.  Why  does  DRY  wood  burn  BETTER  than 
GREEN  ? 

A.  1st — Because  none  of  its  heat  is 
earned  away  by  the  conversion  of  water 
into  steam ;  and 

2dly — The  pores  of  dry  wood  (being 
filled  with  air)  supply  the  fire  with 
oxygen. 

Q.  Why  do  TWO  pieces  of  WOOD  burn  BETTER 
than  ONE  ? 

A.  1st — Because  they  help  to  entan- 
gle the  heat  of  the  passing  smoke,  and 
throw  il  on  the  fuel;  and 

2diy — The  air7  impinging  against  the 
pieces  of  wood,  is  thrown  upon  the  fire 
in  a  kind  of  eddy  or  draught. 

Q.  Why  does  SALT  CRACKLE,  when  thrown 
into  a  FIRE  ? 

A,  Salt  contains  water;  and  the 
crackling  of  the  salt  is  owing  to  the  sud- 
den conversion  of  this  water  into  steam. 

Q.  Why  will  not  wood  or  paper  bwrn  if  steeped 
in  a  solution  of  POTASH,  phosphate  of  LIME,  or  AM- 
MONTA  (hartshorn)  ? 

A.  Because  any  "  alkali "  (such  as 
potash)  will  arrest  the  hydrogen  which 
escapes  from  the  fuel,  and  prevent  its 
Combination  with  the  oxygen  of  air. 

Q.       What  is  an  alkali  ? 

A.     The   con'verse   of  an   acid;    as 
3 


50  CHEMICAL    ACTION. 

bitter  is  the  con'verse  of  sweet,  or  insijjid 
the  con'verse  of  pungent. 

Q.  Why  does  a  JET  of  FLAME  sometimes  burst 
into  the  room  THROUGH  THE  BARS  OF  A  STOVE  ? 

A.  Because  the  iron  bars  conduct 
heat  to  the  interior  of  some  lump  of  coal ; 
and  its  volatile  gas  (bursting-  through 
the  weakest  part)  is  kindled  by  the 
glowing-  coals  over  which  it  passes. 

Q.  Why  is  this  JET  sometimes  of  a  GREENISH 
YELLOW  color  ? 

A.  Either  because  some  lump  of  coal 
lies  over  the  hot  bars ;  or  else  the  coals 
below  it  are  not  red  hot :  in  consequence 
of  which,  some  of  the  g*as  escapes  unburnt, 
and  is  of  a  greenish  color. 

Q.       Why  does  the  gas  escape  UNBURNT  ? 

A.  Because  neither  the  bars,  nor 
coals  over  which  it  passes,  are  red  hot. 

Q.  Why  does  a  BLUISH  FLAME  sometimes  flicker 
on  the  surface  of  hot  cinders  ? 

A.  Because  the  g-as  from  the  hot  coals 
at  the  bottom  of  the  grate,  mixing*  with 
the  carbon  of  the  coals  above,  produces  an 
inflammable  gas  (called  carbonic  oxide), 
which  burns  with  a  blue  flame. 

Q.       Why  is  the  FLAME  of  a  good  fire  YELLOW  ? 

A.  Because  both  the  hydrogen  and 
carbon  of  the  fuel  are  in  a  state  of  perfect 


COMBUSTION.  51 

combustion.  It  is  the  white  heat  of  the 
carbon,  which  gives  the  pale  yellow  tinge 
to  the  flaming  hydrogen. 

Q.       What  is  LIGHT  ? 

A.  Rapid  undulations  of  a  fluid  called 
ether,  striking  on  the  eye. 

Q.  How  does  COMBUSTION  make  these  undula- 
tions of  LIGHT  ? 

A.  The  atoms  of  matter  (set  in  mo- 
tion by  heat)  striking  against  this  ether, 
produce  undulations  in  it ;  as  a  stone 
thrown  into  a  stream,  produces  undula- 
tions in  the  water. 

Q.  How  can  UNDULATIONS  of  ether  produce 
LIGHT? 

A.  As  sound  is  produced  by  undula- 
tions of  air  striking  on  the  ear ;  so  light 
is  produced  by  undulations  of  ether  strik- 
ing on  the  eye. 

Q.       What  is  ETHER  ? 

A.  A  very  subtle  fluid,  which  per- 
vades and  surrounds  everything  we  see. 

N.  B.   This  theory  of  LIGHT  is  not  altogether  satisfactory ; 
but  has  been  retained,  as  the  most  plausible  hitherto  pro- 
*  jected. 

Q.      Does  HEAT  ALWAYS  produce  LIGHT  ? 
A.     No ;  the  heat  of  a  stack  of  hay, 
or  reeking  dunghill,  though  very  great  ^ 
is  not  sufficient  to  produce  light. 

Q.       Why  is  a  YELLOW  FLAME  brighter  than  a 

RED  HOT  COAL  ? 


62  CHEMICAL    ACTION. 

A.  Because  yellow  rays  produce  the 
greatest  amount  of  light,  though  red  rays 
produce  the  greatest  amount  of  heat. 

Q.       Why  is  the  LIGHT  of  a  fire  MORE  INTENSE 
(  sometimes  than  it  is  at  others? 

A.  The  intensity  of  fire-light  depends 
upon  the  whiteness  to  which  the  carbon 
is  reduced  by  combustion.  If  carbon 
be  white  hot,  its  combustion  is  perfect, 
and  the  light  intense;  if  not,  the  light  is 
obscured  by  smoke. 

Q.  Why  will  not  CINDERS  BLAZE,  as  well  as 
FRESH  coals  ? 

A.  The  flame  of  coals  is  made  chiefly 
by  hydrogen  gas.  As  soon  as  this  gas 
has  been  consumed,  the  hot  cinders  pro- 
duce only  a  gas,  called  carbonic  acid, 
which  is  neither  luminous  nor  visible. 

Q.  Where  does  the  hydrogen  gas  of  afire  come 
from? 

A.  All  fuel  is  composed  of  carbon  and 
hydrogen  gas,  which  are  separated  from 
each  other  by  the  process  of  combustion. 
(See  p.  40.) 

Q.  Why  does  not  a  FIRE  BLAZE  on  a  FROSTY 
NIGHT,  so  long  as  it  does  upon  another  night  ? 

A.  1st — Because  air  condensed  by 
the  cold  contains  more  oxygen  than  the 
same  quantity  of  warmer  air ;  and 


COMBUSTION.  53 

2dly  —  Air  condensed  by  the  cold  is 
heavier.  In  consequence  of  which,  it- 
falls  more  quickly  on  the  fire,  to  supply 
the  place  of  the  hot  ascending  air. 

Q.  Why  does  a  FIRE  burn  CLEAREST  on  a 
FROSTY  night  ? 

A.  Because  the  volatile  gases  are 
more  quickly  consumed  ;  and  the  solid 
carbon  is  plentifully  supplied  with  oxygen 
from  the  air,  to  make  it  burn  brightly 
and  intensely. 

Q.  Why  does  a  FIRE  burn  more  intensely  in 
WINTER  than  in  SUMMER  ? 

A.  Because  the  air  is  colder  in  winter, 
than  it  is  in  summer. 

Q.  Why  does  the  COLDNESS  of  the  air  increase 
the  HEAT  of  a  fire? 

A.  1st  —  Because  air  condensed  by 
the  cold,  supplies  more  oxygen  than  a 
similar  volume  of  warmer  air  ;  and 

2d!y  —  Condensed  air,  being  heavy, 
falls  more  rapidly  into  the  place  of  the 
hot  ascending  air,  to  supply  the  fire  with 
nourishment. 


Q.       Why  does  the  SUN,  shining  on  a  FIRE, 
it  DULL  ;  and  often  put  it  out  ? 

A.  1st  —  Because  the  air  (being  rare- 
fied by  the  sunshine)  flows  'more  slowly 
to  theflre  ;  and 


54  CHEMICAL    ACTION. 

2dly — Even  that  which  reaches  the 
fire,  affords  less  nourishment. 

Sunshine  produces  also  some  chemical  eject  upon  the 
air  or  fuel  detrimental  to  combustion. 

Q.  Why  does  the  airflow  to  the  fire  more  TAR- 
DILY for  being  RAREFIED? 

A.  Because  the  greater  the  contmst 
(between  the  external  air  and  that  which 
lias  been  heated  by  the  fire),  the  more  rapid 
will  be  the  current  of  air  toward  that  fire. 

Q.  Why  does  rarefied  air  afford  LESS  NOURISH- 
MENT to  fire  than  cold  air  ? 

A.  Because  rarefied  air  contains  less 
oxygen  than  the  same  quantity  of  con- 
densed air. 

Inasmuch  as  the  same  quantity  of  oxygen  is  diffused 
over  a  larger  volume  of  air. 

Q.  Why  does  a  FIRE  burn  more  fiercely  in  the 
OPEN  AIR? 

A.  1st — Because  the  air  out-of-doors 
is  more  dense  than  the  air  in-doors ;  and 

2dly — It  has  freer  access  to  the  fire. 

Q.  Why  is  the  air  out-of-doors  more  DENSE 
than  that  in-doors  ? 

A.  Because  it  has  freer  circulation ; 
and,  as  soon  as  any  portion  has  been 
rarefied,  it  instantly  escapes,  and  is  sup- 
plied by  colder  currents. 

Q.  Why  does  not  a  FIRE  burn  so  freely  in  a 
THAW  as  in  a  FROST  I 


COMBUSTION.  55 

A.  Because  the  air  is  laden  with 
vapor  ;  in  consequence  of  which,  it  both 
moves  too  slowly,  and  is  too  much  rarefied 
to  nourish  the  fire. 

Q.  Why  does  a  FIRE  burn  so  fiercely  in  WINDY 
weather  ? 

A.  Because  the  air  is  so  rapidly 
changed,  and  affords  plentiful  nourish- 
ment to  the  fire. 

Q.       Why  does  a  pair  of  BELLOWS  get  afire  up  ? 

A.  Because  it  drives  the  air  more  rap- 
idly  to  tliefire ;  and  the  plentiful  supply 
of  oxygen  soon  makes  the  fire  burn  in- 
tensely. 

Q.  Why  is  the  flame  of  a  CANDLE  EXTINGUISHED 
when  blown  by  the  breath ;  and  not  made  more  in- 
tense like  afire? 

A.  Because  the  flame  of  a  candle  is 
confined  to  a  very  small  wick,  from  which 
it  is  severed  by  the  breath ;  and  (being 
unsupported)  must  go  out. 

Q.  Why  is  a  SMOULDERING  WICK  sometimes 
RE-KINDLED  by  blowing  it  ? 

A.  Because  air  is  carried  to  it  by  the 
breath  with  great  rapidity ;  and  the  oxy- 
gen of  the  air  kindles  the  red  hot  wickt 
as  it  would  kindle  charred  wood. 

Q.  Why  is  not  the  red  hot  wick  kindled  by  the 
air  AROUND  &,  without  BLOWING  ? 

A.     Because  oxygen  is  not  supplied 


56  CHEMICAL    ACTION. 

with  sufficient   freedom,  unless  air  be 
blown  to  the  wick. 

Q.  When  is  this  experiment  most  likely  to  suc- 
ceed ? 

A.  In  frosty  weather ;  because  the 
air  contains  more  oxygen  when  it  is 
condensed  by  the  cold. 

Q.  Why  does  a  POKER  LAID  ACROSS  a  dull 
FIRE  revive  it  ? 

A.  For  two  reasons ;  1st — Because 
the  poker  concentrates  the  heat,  and 
therefore  increases  it ;  and 

2dly — Air  is  arrested  in  the  narrow 
aperture  between  the  poker  and  the 
coals,  and  a  draught  created. 

See  p.  49. 

Q.  Why  are  STOVES  fixed  on  the  FLOOR  of  a 
room  ? 

A.  In  order  that  the  air  on  the  lower 
part  of  tlie  room  may  be  heated  by  the 
fire. 

Q.  Would  not  the  air  of  the  lower  part  of  a 
room  be  heated  equally  well)  if  the  stoves  were  fixed 
higher  up  ? 

A.  No ;  the  heat  of  a  fire  has  a  very 
little  effect  upon  the  air  below  tlie  level  of 
tlie  grate;  and,  therefore,  every  grate 
should  be  as  near  to  the  floor  as  possible. 

Q.  Our  FEET  are  very  frequently  COLD  when 
we  sit  dose  by  a  good  fire.  Explain  the  reason  of 
this. 


COMBUSTION.  57 

A.  As  the  fire  consumes  the  air 
which  passes  over  it,  cold  air  rushes 
through  the  crevices  of  the  doors  and 
windows  along  the  bottom  of  the  room 
to  supply  the  deficiency  ;  and  these  cur 
rents  of  cold  air,  rushing  constantly  over 
our  feet,  deprive  them  of  their  warmth. 

Q.  If  a  piece  of  PAPER  be  laid  FLAT  on  a  clear 
fire,  it  will  NOT  BLAZE  but  CHAR.  Why  so? 

A.  Because  the  carbon  of  a  clear  fire, 
being-  sufficiently  hot  to  unite  with  the 
oxygen  of  the  air,  produces  carbonic  acid 

fas,  which  soon  envelops  the  paper  laid 
at  upon  the  cinders :  but  carbonic  acid 
gas  will  not  blaze. 

Q.  If  you  BLOW  the  paper,  it  will  BLAZE  im- 
mediately. Why  so  ? 

A.  Because  by  blowing  or  opening  a 
door  suddenly,  the  carbonic  acid  is  dissi- 
pated^ and  the  paper  fanned  into  flame. 

Q.       Why  does  WATER  EXTINGUISH  a  FIRE  ? 

A.  1st — Because  the  water  forms  a 
coating  over  the  fuel,  which  keeps  it  from 
the  air ;  and 

2dly — The  conversion  of  water  into 
steam,  draws  off  the  heat  of  the  burning 
fuel. 

Q.  A  LITTLE  WATER  mcikes  a  fire  FIERCER, 
while  a  LARGER  quantity  of  water  puts  it  OUT.. 
Explain  how  this  is. 

3* 


58  CHEMICAL    ACTION. 

A.  Water  is  composed  of  oxygen  and 
hydrogen;  when,  therefore,  the  fire  can 
decompose  the  water  into  its  simple  ele- 
ments, it  serves  for  fuel  to  the  flame. 

Q.       How  can  WATER  serve  for  FUEL  to  fir  el 

A.  Because  the  hydrogen  of  the  water 
burns  with  aflame ;  and  the  oxygen  of  the 
water  increases  the  intensity  of  that 
flame. 

Q.  When  a  house  is  on  fire,  is  too  LITTLE  water 
worse  than  NONE  ? 

A.  Certainly.  Unless  water  be  sup- 
plied so  plentifully  as  to  quenck  the  fire, 
it  will  increase  its  intensity,  like  fuel. 

Q.       When  will  water  EXTINGUISH  FIRE  ? 

A.  When  the  supply  is  so  rapid  and 
abundant  that  the  fire  cannot  decompose 
it. 

Q.  Does  not  a  very  LITTLE  water  SLACKEN  the 
heat  of  fire  ? 

A.  Yes,  till  it  is  decomposed ;  it  then 
increases  the  intensity  of  fire,  and  acts 
like  fuel. 

Q.  Why  does  the  WICK  of  a  candle  (when  the 
flame  has  been  blown  out)  very  readily  CATCH  FIRE? 

A.  Because  the  wick  is  already  hot, 
and  a  very  little  extra  heat  will  throw  it 
into  flame. 

Q,       Why  does  the  EXTRA  heat  revive  the  flame? 


COMBUSTIOX.  59 

A.  Because  it  again  liberates  the 
hydrogen  of  the  tallow,  and  ignites  it. 

Q.  Cannot  WOOD  be  made  to  BLAZE  without 
actual  contact  with  fire  ? 

A.  Yes;  if  a  piece  of  wood  be  held 
near  the  fire  for  a  little  time,  it  will  blaze, 
even  though  it  does  not  touch  the  fire. 

Q.  Why  will  WOOD  BLAZE,  even  if  it  does  not 
touch  the  fire  ? 

A.  Because  the  heat  of  the  fire 
drives  out  the  hydrogen  gas  of  the  wood  ; 
which  gas  is  inflamed  by  contact  with 
the  red  hot  coals. 

Q.  Why  will  a  NEIGHBOR'S  HOUSE  sometimes 
CATCH  FIRE,  though  no  flame  of  the  burning  house 
ever  touches  it  ? 

A.  Because  the  heat  of  the  burning 
house  sets  at  liberty  the  hydrogen  gas  of 
the  neighboring  wood- work  ;  and  this 
gas  is  ignited  by  the  flames  or  red  hot 
bricks  of  the  house  or  fire. 

Q.       What  is  COKE  ? 

A.  Coal  freed  from  its  volatile  gases 
by  the  action  of  artificial  heat. 

Q.  Why  do  STOVES  sometimes  SMELL  very 
strongly  ^SULPHUR? 

A.  Because  coal  and  coke  contain 
sulphur ;  and  whenever  the  draught  is 
not  rapid  enough  to  drive  the  sulphur  up 
the  flue,  it  is  emitted  into  the  room. 


60  CHEMICAL    ACTION. 

Q.  What  is  meant  by  SPONTANEOUS  COMBUS- 
TION ? 

A.  Combustion  produced  without  the 
application  of  flame. 

Q.       Give  an  example  of  spontaneous  combustion. 

A.  Coals  stowed  in  the  hold  of  a 
vessel,  and  goods  packed  in  a  warehouse, 
will  often  catch  fire  of  themselves — espe- 
cially such  goods  as  cotton,  flax,  hemp, 
rags,  &c. 

Q.  Why  do  such  GOODS  sometimes  CATCH  FIRE 
of  themselves  ? 

A.  Because  they  are  piled  together 
in  very  large  masses  in  a  damp  state  or 
place. 

Q.  Why  does  this  produce  spontaneous  combus- 
tion ? 

A.  The  damp  produces  dzcay,  or  the 
decomposition  of  the  goods ;  and  the 
great  heat  of  the  piled-up  mass  makes 
the  decaying  goods  ferment. 

Q.  How  does  this  FERMENTATION  produce  COM- 
BUSTION ? 

A.  During  fermentation,  carbonic  acid 
gas  is  given  off  by  the  goods — a  slow 
combustion  ensues — till  at  length  the 
whole  pile  bursts  into  flame. 

Q.  Wh.y  is  the  HEAT  of  a  LARGE  MASS  of  goods 
GREATER  than  that  of  a  smaller  quantity  ? 

A.     Because  the  carbonic  acid  cannot 


COMBUSTION.  61 

escape  through  the  massive  pile ;  and 
the  products  of  decomposition  being  con- 
fined, hasten  further  changes. 

Q.  Why  do  HAY-STACKS  sometimes  CATCH  FIRE 
of  themselves  ? 

A.  Either  because  the  hay  was  got 
up  damp  ;  or  else  because  rain  has  pen- 
etrated the  stack. 

Q.  Why  will  a  HAY-STACK  CATCH  FIRE  if  the 
hay  be  damp  ? 

A.  Because  damp  hay  soon  decays, 
and  undergoes  a  state  of  fermentation ; 
during  which,  carbonic  acid  gas  is  given 
off,  and  the  stack  catches  fire. 

Q.  Roasted  COFFEE  sometimes  CATCHES  fire 
spontaneously.  Explain  the  reason  of  this. 

A.  The  heat  of  coffee  is  greatly  in- 
creased by  being  roasted;  and  the  car- 
bon of  the  coffee,  uniting  with  the  oxygen 
of  the  air,  produces  carbonic  acid  gas,  and 
bursts  \ntoflame. 

Q.  Why  do  old  RAGS,  used  for  CLEANING 
LAMPS  and  CANDLESTICKS,  sometimes  set  a  HOUSE  on 
fire? 

A.  Because  they  very  readily  fer- 
ment, and  (during  fermentation)  throw 
off  exceedingly  inflammable  gases. 

N.  B.  Lamp-black  mixed  with  linseed  oil  is  more  liable 
to  spontaneous  combustion  than  anything  that  servants 
handle.  . 


62  CHEMICAL    ACTION. 


CHAPTER   Y. 

/  .         SMOKE. 

Q.       Why  does  SMOKE  ASCEND  the  chimney  ? 

A.  Because  the  air  of  the  room  (when 
it  passes  over  the  fire)  becomes  lighter 
for  being*  heated  ;  and  (being-  thus  made 
lighter')  ascends  the  chimney,  carrying 
the  smoke  with  it. 

Q.       What  is  SMOKE? 

A.  Small  particles  of  carbon,  separat- 
ed by  combustion  from  the  fuel,  but  not 
consumed. 

Q.  Why  do  SMOKE  and  steam  CURL  as  they 
ascend  ? 

A.  Because  they  are  pushed  round 
and  round  by  the  ascending  and  de- 
scending currents  of  air. 

Q.  Why  does  a  CLOSE  STOVE  DRAW  up  more 
fiercely  than  an  OPEN  GRATE  ? 

A.  Because  the  air  which  supplies 
the  stove  must  pass  through  the  fire ; 
and,  as  it  becomes  exceedingly  heated, 
rushes  up  the  flue  with  great  violence. 

Q.  What  produces  the  ROARING  noise  made  by 
the  fire  in  a  close  stove? 

A.  Air  rushing  rapidly  through  the 
crevices  of  the  iron  door,  and  up  the 
chimney  flue. 


SMOKE.  63 

Q.  Why  is  the  ROAR  LESS  if  the  stove  DOOR  be 
thrown  OPEN? 

A.  Because  fresh  air  gets  access  to 
the  fire  more  easily ;  and,  as  the  air  is 
not  so  intensely  heated,  its  motion  is  not 
so  violent. 

Q.       Why  do  some  CHIMNEYS  SMOKE  ? 

A.  Because  fresh  air  is  not  admitted 
into  a  room  so  fast  as  it  is  consumed  by 
the  fire ;  in  consequence  of  which,  a  cur- 
rent of  air  rushes  down  the  chimney  to 
supply  the  deficiency,  driving*  the  smoke 
along-  with  it 

Q.       Explai7i  this  by  an  illustration. 

A.  If  water  be  taken  with  a  pail  out 
of  a  river,  other  water  will  rush  toward 
the  hole  as  soon  as  the  pail  is  lifted  out ; 
and,  if  air  be  taken  from  a  room  (as  it 
is,  when  some  of  it  g*oes  up  the  chimney), 
other  air  will  rush  toward  the  void  to 
fill  it  up. 

Q.  What  prevents  air  being  supplied  so  fast  as 
it  is  consumed  by  the  fire  ? 

A.  Leather  and  curtains  round  the 
doors:  sand-bag's  at  the  threshold  and 
on  the  window-frames;  and  other  con- 
trivances to  keep  out  the  draug-ht. 

Q.       Why  will  the  air  come  down  the  CHIMNEY  ? 

A.     Because  it  can  g-et  into  the  room 


64  CHEMICAL    ACTION. 

,n  no  other  way,  if  the  doors  and  win- 
dows are  all  made  air -tight. 

Q.       What  is  the  best  REMEDY  in  such  a  case  ? 

A.  The  speediest  remedy  is  to  open 
the  door  or  window :  but  by  far  the  best 
remedy  is  to  carry  a  small  tube  from  the 
hearth  into  the  external  air. 

Q.       Why  is  that  the  BEST  remedy  ? 

A.  Because  the  fire  will  be  plenti- 
fully supplied  with  air  by  the  tube :  the 
doors  and  windows  may  all  remain  air- 
tight ;  and  we  may  enjoy  a  warm  fire- 
side, without  the  inconvenience  of 
draughts  and  cold  feet. 

Q.  Why  is  a  CHIMNEY  raised  so  high  above 
the  ROOF? 

A.  That  it  may  not  smoke ;  as  all 
funnels  do  which  are  too  short. 

Q.  What  is  meant  by  the  FUNNEL  or  FLUE  of 
a  chimney  ? 

A.  That  part  of  a  chimney  through 
which  the  smoke  passes. 

Q.  Why  does  a  CHIMNEY  SMOKE,  if  the  funnel 
be  very  short  ? 

A.  Because  the  draught  of  a  short 
flue  is  too  slack  to  carry  the  smoke  up 
the  chimney. 

Q.  Why  is  the  DRAUGHT  of  a  SHORT  FLUE 
more  SLACK  than  that  of  a  long  one  ? 


SMOKE. 


A.  1st — Because  the  fire  is  always 
dull  and  sluggish,  if  the  chimney  be  too 
short : 

2dly — Because  the  smoke  rolls  out  of 
the  chimney,  before  it  has  acquired  its 
full  velocity  ;  and 

3dly — Because  the  wind,  rain,  and  air, 
have  more  influence  over  a  short  funnel, 
than  over  a  long  one. 

Q.  Why  is  the  FIRE  always  DULL  and  SLUG- 
GISH, if  the  CHIMNEY-FLUE  be  very  SHORT? 

A.  Because  the  draught  is  bad ;  and, 
as  the  rarefied  air  passes  very  tardily  up 
the  chimney — fresh  air  flows  as  tardily 
toward  the  fire,  to  supply  it  with  oxygen. 

Q.       On  what  does  the  INTENSITY  of  fire  depend? 

A.  The  intensity  of  fire  is  always  in 
proportion  to  the  quantity  of  oxygen  with 
which  it  is  supplied. 

Q.  Why  does  not  SMOKE  acquire  its  full  VELO- 
CITY in  a  SHORT  funnel* 

A.  Because  the  higher  smoke  as- 
cends, (provided  the  flue  be  clear  and 
hot,)  the  faster  it  goes :  if,  therefore,  a 
funnel  be  very  short,  the  smoke  never 
acquires  its  full  velocity. 

Q.  Does  the  DRAUGHT  of  a  chimney  depend  on 
the  SPEED  of  the  SMOKE  through  the  flue? 

A.  Yes.  The  more  quickly  hot  air 
flies  up  the  chimney,  the  more  quickly 


66  CHEMICAL    ACTION. 

cold  air  will  rush  toward  the  fire  to  supply 
the  place ;  and,  therefore,  the  longer  the 
flue,  the  greater  the  draught. 

Q.  Why  are  the  CHIMNEYS  of  MANUFACTORIES 
made  so  very  LONG  ? 

A.  To  increase  the  intensity  of  the 
fire. 

Q.       Why  is  the  INTENSITY  of  a  fire  increased  by 

LENGTHENING  the  FLUE  ? 

A.  Because  the  draught  being*  great- 
er, more  fuel  is  consumed  in  the  same 
time  ;  and,  of  course,  the  intensity  of  the 
heat  is  proportionally  greater. 

Q.  If  a  SHORT  CHIMNEY  cannot  be  lengthened, 
what  is  the  best  REMEDY  to  prevent  smoking  ? 

A.  To  contract  the  opening  of  tlie 
chimney  contiguous  to  the  stove. 

Q.  Why  will  a  SMALLER  OPENING  against  the 
stove  PREVENT  the  chimney's  SMOKING  ? 

A.  Because  the  air  will  be  compelled 
to  pass  nearer  the  fire  ;  and  (being  more 
heated)  will  rise  through  the  chimney 
more  rapidly.  This  increase  of  heat  will 
therefore  compensate  for  the  slwrtness 
of  the  flue. 

Q.  Why  will  a  ROOM  SMOKE  if  there  be  TWO 
FIRES  in  it  ? 

A.  Because  the  fiercer  fire  will  ex- 
haust the  most  air,  and  draw  from  the 
smaller  one,  to  supply  its  demand. 


SMOKE.  67 

Q.  Why  will  a  chimney  SMOKE  if  there  be  a 
FIRE  in  TWO  ROOMS  communicating  with  each  other? 

A.  Because  (whenever  the  d'jor  be- 
tween the  two  rooms  is  opened)  air  will 
rush  from  the  chimney  of  the  inferior 
fire  to  supply  the  other  ;  and  both  rooms 
will  be  filled  with  smoke. 

Q.       What  is  the  best  REMEDY  in  this  case  ? 

A.  Let  a  tube  be  carried  from  the 
hearth  of  each  stove  into  the  external 
air ;  and  then  each  fire  will  be  so  well 
supplied,  that  neither  will  need  to  bor- 
row from  the  other. 

Q.  Why  does  a  HOUSE  in  a  VALLEY  or  by  the 
side  of  higher  buildings  very  often  SMOKE  ? 

A.  Because  the  wind  (striking* 
against  the  surrounding*  hills  or  building's) 
bounds  back  again  upon  the  chimney :  and 
destroys  its  draug-ht. 

Q.       What  is  the  REMEDY  in  these  cases  ? 

A.  To  fix  a  cowl  on  the  chimney-top, 
to  turn  like  a  weather-cock,  and  present 
its  back  to  the  wind. 

Q.  Why  will  not  a  COWL  always  PREVENT  a 
chimney  SMOKING? 

A.  Because  if  the  wind  be  strong,  it 
will  keep  the  opening  of  the  cowl  toward 
the  higher  building  or  hill ;  and  then  the 
reflected  wind  will  blow  into  the  cowl, 
and  down  the  chimney. 


68  CHEMICAL    ACTION. 

Q.  As  a  cowl  is  suck  a  poor  remedy,  can  any 
OTHER  be  suggested  ? 

A.  Yes.  If  the  chimney-flue  can  be 
carried  higher  than  the  other  building's 
or  hills,  no  wind  can  enter  the  flue. 

Q.  If  a  chimney -flue  be  carried  up  HIGHER  than 
the  buildings  or  hill,  why  cannot  the  wind  enter  it  ? 

A.  Because  the  reflected  wind  would 
strike  against  the  sides  of  the  chimney- 
flue,  and  not  pass  over  the  opening  at  all. 

Q.       In  what  OTHER  cases  will  a  CHIMNEY  SMOKE  ? 

A.  If  the  door  and  stove  are  both 
placed  on  the  same  side  of  a  room,  the 
chimney  will  often  smoke. 

Q.  Why  will  a  CHIMNEY  SMOKE,  if  the  DOOR 
and  STOVE  are  both  on  the  SAME  SIDE  ? 

A.  Because  (whenever  the  door  is 
opened)  a  current  of  air  will  blow  ob- 
liquely into  the  chimney-place,  and  drive 
the  smoke  into  the  room. 

Q.       What  REMEDY  can  be  applied  to  this  evil? 

A.  The  door  must  be  set  opposite  to 
the  chimney-place,  or  nearly  so;  and 
then  the  draught  from  the  door  wUl  blow 
the  smoke  up  the  chimney,  and  not  into 
the  room. 

Q.  Why  will  a  CHIMNEY  SMOKE  if  it  NEEDS 
SWEEPING  ? 

A.     Because  loose  soot  obstructs  the 


SMOKE.  69 

free   passage  of  the  smoke,  delays  its 
current,  and  prevents  the  draught. 

Q.  Why  will  a  CHIMNEY  SMOKE  if  it  be  OUT 
OF  REPAIR  ? 

A.  1st — Because  the  loose  mortar  and 
bricks  obstruct  the  smoke  ;  and 

2dly — Cold  air  (oozing-  through  the 
chinks)  chills  the  air  in  the  chimney,  and 
prevents  its  ascent. 

Q.  Why  will  a  STOVE  SMOKE,  if  the  joints  of 
the  flue  do  not  Jit  air-tight? 

A.  Because  cold  air  (oozing  through 
the  joints)  chills  the  air  in  the  flue,  and 
prevents  its  ascent. 

Q.  Why  does  an  old-fashioned  FARM  CHIMNEY- 
PLACE  generally  smoke  ? 

A.  Because  the  opening  is  so  very 
large,  that  much  of  the  air  which  goes 
up  the  chimney,  has  never  passed  near 
the  fire ;  and  this  cold  air  (mixing  with 
the  hot)  so  reduces  its  temperature  that  it 
ascends  very  slowly,  and  the  draught  is 
destroyed. 

Q.  Why  does  a  chimney  smoke  if  the  DRAUGHT 
be  SLACK  ? 

A.  Because  the  current  of  air  up  the 
chimney  is  not  powerful  enough  to  buoy 
up  the  smoke  through  the  flue. 

Q.  If  the  opening  of  a  chimney  be  TOO  LARGE, 
what  REMEDY  can  be  applied  ? 


70  CHEMICAL    ACTION. 

A.  The  chimney-place  must  be  con- 
tracted. 

Q.       Why  will  CONTRACTING  the  chimney -place 

PREVENT  itS  SMOKING  ? 

A.  Because  the  air  will  then  pass 
nearer  the  fire  ;  and  (being  more  heated) 
fly  faster  up  the  chimney. 

Q.  Why  do  almost  all  CHIMNEYS  SMOKE  in 
GUSTY  weather  ? 

A.  Because  the  column  of  smoke  is 
suddenly  chilled  by  the  wind,  and  (be- 
ing* unable  to  ascend)  rushes  back  into 
the  room. 

Q.       What  is  the  use  of  a  CHIMNEY-POT? 

A.  It  serves  to  increase  the  draught, 
when  the  opening  of  a  chimney  is  too 
large. 

Q.  How  does  a  CHIMNEY-POT  INCREASE  the 
DRAUGHT  of  a  chimney  ? 

A.  As  the  same  quantity  of  hot  air 
has  to  escape  through  a  smaller  opening, 
it  must  pass  through  more  quickly. 

Q.       Why  do  BLOWERS  help  to  get  afire  up  ? 

A.  Because  they  compel  the  air  to 
go  through  the  fire,  and  not  over  it; 
in  consequence  of  which,  the  fire  is  well 
supplied  with  oxygen,  and  the  draught 
greatly  increased. 

Q.       Why    does    a    BLOWER     INCREASE     the 

DRAUGHT  ? 


SMOKE.  71 

A.  Because  the  air  (by  passing 
through  the  fire)  is  made  much  hotter, 
and  ascends  the  chimney  more  rapidly. 

Q.  Why  is  a  fire  better  supplied  with  oxygen 
while  the  blower  hangs  before  it  ? 

A.  Because  the  blower  increases  the 
draught ;  and  the  faster  the  hot  air  flies 
up  the  cliimney,  the  faster  will  cold  air 
rush  toward  the  fire,  to  supply  it  with 
oxygen. 

Q.       WTiy  does  a  parlor  often  SMELL  disagreeably 

Of  SOOT  in  SUMMER,-TIME? 

A.  Because  the  air  in  the  chimney 
(being  colder  than  the  air  in  the  parlor) 
descends  into  the  room,  and  leaves  a  dis- 
agreeable smell  of  soot  behind. 

Q.  Why  are  the  CEILINGS  of  PUBLIC  OFFICES 
generally  BLACK  and  filthy  ? 

A.  Because  the  heated  air  of  the 
office  buoys  up  the  dust  and  fine  soot ; 
which  (being  unable  to  escape  through 
the  plaster)  is  deposited  on  the  ceiling. 

Q.  Why  are  SOME  parts  of  the  ceiling  BLACKER 
and  more  filthy  than  others? 

A.  Because  the  air,  being  unable  to 
penetrate  the  thick  joists  of  the  ceiling 
passes  by  those  parts,  and  deposits  its  soot 
and  dust  on  others  more  penetrable. 

N.  B.    The  site  of  this  deposit  of  soot  and  dust  is  fre- 
quently determined  by  draughts  and  currents  of  air. 


72  CHEMICAL    ACTION. 

Q.       What  is  CHARCOAL  ? 

A.  Wood  which  has  been  exposed  to 
a  red  heat,  till  it  has  been  deprived  of 
all  its  gases  and  volatile  parts. 

Q.  Why  is  a  CHARCOAL  FIRE  hotter  than  a 
wood  fire? 

A.  Because  charcoal  is  very  pure 
carbon  ;  and,  as  it  is  the  carbon  of  fuel 
which  produces  the  glowing*  heat  of 
combustion,  therefore,  the  purer  the  car- 
bon, the  more  intense  will  the  heat  of 
the  fire  be. 

Q.  Why  does  charcoal  REMOVE  the  TAINT  of 
meat  ? 

A.  Because  it  absorbs  all  putrescent 
effluvia,  whether  they  arise  from  animal 
or  vegetable  matter. 

Q.  Why  is  WATER  PURIFIED  by  being  filtered 
through  charcoal  ? 

A.  Because  charcoal  absorbs  the  im- 
purities of  the  water,  and  removes  all 
disagreeable  tastes  and  smells,  whether 
they  arise  from  animal  or  vegetable 
matter. 

Q.  Why  are  water  and  wine  CASKS  CHARRED 
inside  ? 

A.  Because  charring  the  inside  of 
a  cask  reduces  it  to  a  kind  of  charcoal ; 
and  charcoal  (by  absorbing  animal  and 


SMOKE.  73 

vegetable  impurities)  keeps  the  liquor 
sweet  and  good. 

Q.  Why  does  a  piece  of  BURNT  BREAD  make 
impure  WATER  fit  to  drink  ? 

A.  Because  the  surface  of  the  bread 
(which  has  been  reduced  to  charcoal  by 
being-  burnt)  absorbs  the  impurities  of  the 
water,  and  makes  it  palatable. 

Q.  Why  should  TOAST  and  WATER,  placed  by 
the  side  of  the  sick,  be  made  of  BURNT  BREAD? 

A.  Because  the  charcoal  surface  of 
burnt  bread  prevents  the  water  from 
being  affected  by  the  impurities  of  the 
sick  room, 

Q.  Why  should  sick  persons  eat  DRY  TOAST 
rather  lhan  bread  and  butter  ? 

A.  Because  the  charcoal  surface  of 
the  dry  toast  helps  to  absorb  the  acids 
and  impurities  of  a  sick  stomach, 

There  are  other  reasons  which  belong  to  the  science  of 
medicine. 

Q.  Why  are  TIMBERS  which  are  to  be  exposed 
to  damp  CHARRED  ? 

A.  Because  charcoal  undergoes  no 
change  by  exposure  to  air  and  water ;  in 
consequence  of  which,  timber  will  resist 
weather  much  longer  after  it  has  been 
charred. 


74  CHEMICAL    ACTION. 

CHAPTER   VI. 

LAMPS   AND   CANDLES. 

Q.  Of  what  are  OIL,  TALLOW,  and  WAX  com 
posed  ? 

A.  Principally  of  carbon  and  hydro- 
gen  gas.  The  solid  part  is  carbon,  the 
volatile  part  is  hydrogen  gas. 

Q.       What  is  CARBON  ? 

A.  A  solid  substance,  generally  of  a 
black  color;  well  known  under  the 
forms  of  charcoal,  lamp-black,  coke,  &c. 

Q.       What  is  HYDROGEN  GAS  ? 

A.  The  principal  ingredient  of  water. 
It  burns  so  readily  that  it  used  to  be 
called  "  inflammable  air."* 

Common  coal  gas  is  a  mixture  of  carbon  and  hydrogen, 
called  "  carburetted  hydrogen."    See  p.  262. 

Q.  A  CANDLE  BURNS  when  lighted.  Explain 
how  this  is. 

A.  The  heat  of  the  lighted  wick  de- 
composes the  tallow  into  its  elementary 
parts  of  carbon  and  hydrogen ;  and  the 
hydrogen  of  the  tallow,  combining  with 
the  oxygen  of  the  air,  produces  flame. 

Q.  WHERE  is.  the  tallow  or  wax  of  a  candle 
decomposed  ? 

A.     In  the  wick.     The  melted  tallow, 

*  To  make  hydrogen  gas,  see  p.  41. 


LAMPS    AND    CANDLES.  75 

or  wax,  rises  up  the  wick  by  capillary 
attraction,  and  is  rapidly  decomposed  by 
the  heat  of  the  flame. 

Q.       What  is  capillary  attraction  ? 

A.  The  power  which  very  minute 
tubes  possess  of  causing  a  liquid  to  rise 
in  them  above  its  level. 

"Capillary."  from  the  Latin  word  "capillaris"  (like  a 
hair}  ;  the  tubes  referred  to  are  almost  as  fine  and  delicate 
as  a  hair. 

Water  ascends  through  a  lump  of  sugar,  or  piece  of 
sponge,  by  capillary  attraction.  N.  B. — The  smaller  a 
tube,  the  higher  will  a  liquid  be  attracted  by  it. 

Q.       Why  is  the  FLAME  of  a  candle  HOT? 

A.  Because  the  flame  liberates  latent 
heat  from  the  air  and  tallow. 

Q.       How  is  LATENT  HEAT  liberated  by  the  flame 

of  a  CANDLE? 

A.  When  the  elements  of  the  tallow 
combine  with  the  oxygen  of  the  air,  latent 
heat  is  liberated  by  the  chemical  changes. 

Q.       Why  does  the  flame  of  a  CANDLE  produce 

LIGHT  ? 

A.  Because  the  chemical  changes 
made  by  combustion  excite  undulations 
of  ether,  which  (striking  the  eye)  produce 
light. 

See  p.  51. 
Q.       Why  is  theflame^  of  a  CANDLE  YELLOW  ? 

A.  It  is  not  so  altogether  ;  only  the 
outer  coat  of  the  flame  is  yellow — the 


76  CHEMICAL    ACTION. 

lower  part  is  violet ;  and  the  inside  of  the 
flame  hollow. 

Q.       Why  is  the  outside  of  the  flame  YELLOW  ? 

A.  Because  the  carbon  of  the  tallow 
(being*  in  a  state  of  perfect  combustion) 
is  made  white  hot. 

See  p.  50. 

Q.  Why  is  the  BOTTOM  part  of  the  flame  pur- 
ple? 

A.  Because  it  is  overladen  with  hydro- 
gen,  raised  from  the  tallow  by  the  burn- 
ing- wick ;  and  this  gas  (which  burns 
with'a  blue  flame)  gives  the  dark  tinge 
to  the  bottom  of  the  candle-flame. 

Q.       Why  is  the  INSIDE  of  the  flame  HOLLOW? 

A.  Because  it  is  fllled  with  vapor, 
raised  from  the*  candle  by  the  Jieat  of  the 
wick,  and  not  yet  reduced  to  a  state  of 
combustion. 

Q.  Describe  the  different  parts  of  the  FLAME  of 
a  common  CANDLE. 

A.  The  flame  consists  of  three  cones. 
The  innermost  cone  is  hollow ;  the  inter- 
mediate one  of  a  dingy  purple  hue;  and 
the  outside  cone  is  yellow. 

Q.  Why  is  the  intermediate  cone  of  a  flame 
PUHPLE  as  well  as  the  BOTTOM  of  the  flame? 

A.  Because  the  gases  are  not  in  a 
state  of  perfect  combustion ;  but  contain 


LAMPS    AND    CANDLES.  77 

an  excess  of  hydrogen,  which  gives  the 
flame  a  purple  tinge. 

Q.  Why  is  not  the  MIDDLE  cone  in  a  state  of 
perfect  combustion  as  well  as  the  outer  one  ? 

A.  Because  the  outer  cone  prevents 
the  oxygen  of  the  air  from  getting  to  the 
middle  of  the  flame ;  and  without  the 
free  access  of  oxygen  gas,  there  is  no 
such  thing  as  complete  combustion. 

Q.  Why  does  the  FLAME  of  a  candle  point  UP- 
WARDS ? 

A.  Because  it  heats  the  surrounding 
air,  which  (being  hot)  rapidly  ascends, 
driving  the  flame  upwards  at  the  same 
time. 

Q.  Wh.y  is  the  FLAME  of  a  candle  POINTED  at 
the  lop  like  a  cone  ? 

A.  Because  the  upper  part  of  a  flame 
is  more  volatile  than  the  lower;  and,  as 
it  affords  less  resistance  to  the  air,  is  re- 
duced to  a  mere  point. 

Q.  Why  are  the  LOWER  parts  of  a  flaine  less 
VOLATILE  than  the  upper? 

A.  Because  they  are  laden  with  un- 
consumed  gas  and  watery  vapor,  which 
present  considerable  resistance  to  the  air. 

Q.  Why  is  the  FLAME  of  a  candle  BLOWN  OUT 
by  a  puff  of  breath  ? 

A.  Because  it  is  severed  from  the 
wick,  and  goes  out  for  want  of  support. 


78  CHEMICAL    ACTION. 

Q.  Why  does  the  FLAME  of  a  candle  make  A 
GLASS  (which  is  held  over  it)  DAMP  ? 

A.  Because  a  "  watery  vapor "  is 
made  by  the  combination  of  the  hydrogen 
of  the  tallow  with  the  oxygen  of  the  air  ; 
and  this  "  vapor  "  is  condensed  by  the 
cold  glass  held  above  the  flame. 

Q.  Why  does  our  hand,  held  ABOVE  a  candle, 
suffer  more  from  heat  than  when  it  is  placed  BELOW 
the  flame,  or  on  ONE  SIDE  of  it? 

A.  Because  the  hot  gases  and  air 
(in  their  ascent)  come  in  contact  with  the 
hand  placed  above  the  flame ;  but  when 
the  hand  is  placed  below  the  flame,  or  on 
one  side,  it  only  feels  heat  from  radiation. 

Radiation:  i.  e.,  emission  of  rays.  The  candle-flame 
throws  out  rays  of  light  and  heat  in  all  directions ;  but 
when  the  hand  is  held  above  the  flame,  it  not  only  feels  the 
heat  of  the  rays,  but  also  of  the  ascending  current  of  hot 
air,  &c. 

Q.  Why  is  a  RUSH  LIGHT  extinguished  more 
quickly  than  a  cotton-wick  candle  ? 

A.  Because  a  hard  rush  imbibes  the 
melted  fat  or  wax  much  more  slowly 
than  porous,  cotton ;  as  it  imbibes  less 
fat,  it  supplies  a  smaller  volume  of  com- 
bustible gases ;  and,  of  course,  the  light 
is  more  easily  extinguished. 

Q.  Why  is  it  more  difficult  to  blow  out  a  COT- 
TON wick  thai/i  a  rush  light? 

A.     Because   porous   cotton   imbibes 


LAMPS    AND   CANDLES.  79 

the  melted  fat,  or  wax,  much  more  quick- 
ly than  hard  rush  ;  as  it  imbibes  more 
fat,  it  supplies  the  flame  with  a  larger 
volume  of  combustible  gases;  and,  of 
course,  the  light  is  with  more  difficulty 
extinguished. 

Q.  Why  is  a  GAS  FLAME  more  easily  extin- 
guished when  the  jet  is  very  slightly  turned  on^  than 
when  it  is  in  full  stream  ? 

A.  Because  there  is  less  volume  of 
combustible  gases  in  the  small  flame 
than  in  the  full  blaze. 

Q.  Why  does  an  EXTINGUISHER  put  a  candle 
out? 

A.  Because  the  air  in  the  extin- 
guisher is  soon  exhausted  of  its  oxygen  by 
the  flame :  and  when  there  is  no  oxy- 
gen, flame  goes  out. 

Q.  Why  does  not  a  candle  set  fire  to  a  PIECE 
of  PAPER  twisted  into  an  extinguisher,  and  used  as 
such  ? 

A.  1st — Because  the  flame  very  soon 
exhausts  the  oxygen  contained  in  the  pa- 
per extinguisher  :  and 

2dly  —  The  flame  invests  the  inside 
of  the  paper  extinguisher  with  carbonic 
acid  gas,  which  prevents  it  from  blazing. 

Q.       Why  is  a  LONG  WICK  never  upright  ? 

A.  Because  it  is  bent  by  its  own 
weight. 


80  CHEMICAL    ACTION. 

Q.  A  LONG  WICK  is  covered  with  an  EFFLORES- 
CENCE at  the  top.  .  What  doas  this  arise  from  ? 

A.  The  knotty  or  flowery  appear- 
ance of  the  top  of  a  wick  arises  from  an 
accumulation  of  particles  partly  separat- 
ed but  still  loosely  hanging*  to  the  wick. 

Q.  Why  is  not  the  END  of  a  long  wick  BURNT 
OFF  as  it  hangs  over  the  fame  ? 

A.  Because  the  length  of  the  wick 
diminishes  the  heat  of  the  flame ;  so  that 
it  is  no  longer  hot  enough  to  consume  the 
wick. 

Q.  Why  do  PALMER'S  METALLIC  WICKS  never 
need  SNUFFING  ? 

A.  Because  the  wick  is  divided  into 
two  parts,  each  of  which  bends  toward 
the  outside  of  the  flame,  where  the  end 
is  intensely  heated,  and  separated  from  the 
wick  by  the  current  of  air  up  the  candle. 

N.  B.   The  small  wire  twisted  in  the  wick  greatly  assists 
the  process. 

Q.  Why  do  common  CANDLES  require  to  be 
SNUFFED  ? 

A.  Because  the  heat  of  the  flame  is 
not  sufficient  to  consume  the  wick ;  and 
the  longer  the  wick  grows,  the  less  heat 
the  flame  produces. 

Q.       Why  do  WAX  CANDLES  NEVER  need  SNUFF- 
ING? 
A.     Because  the  wick  of  wax  candles 


LAMPS    AND   CANDLES.  81 

is  made  of  very  fine  thread,  which  the 

heat  of  the  flame  is  sufficient  to  consume. 

The  wick  of  tallow  candles  (on  the  other 

1  hand)  is  made  of  coarse  cotton,  which  is 

1  too  substantial  to  be  consumed  by  the 

\  heat  of  the  flame,  and  must  be  cut  off 

]  by  snuffers. 

Q.       Why  does  a  PIN  stuck  in  a  RUSH  LIGHT 

s    EXTINGUISH  it?  , 

A.  Because  a  pin  (being1  a  good 
]  conductor)  carries  away  the  heat  of  the 
\  fiame  from  the  ivick,  and  prevents  the 
1  combustion  of  the  tallow. 

Q.       What  is  the  SMOKE  of  a  CANDLE  ? 

A.  Solid  particles  of  carbon,  separat- 
ed from  the  wick  and  tallow,  but  not 
consumed. 

Q.  Why  are  SOME  particles  consumed  and  not 
OTHERS  ? 

A.  The  combustion  of  the  carbon  de- 
pends upon  its  combining  with  the  oxygen 
of  the  air :  now,  as  the  outer  surface  of 
the  flame  prevents  the  access  of  air  to  the 
interior  parts,  much  of  the  carbon  of 
those  parts  passes  off  in  smoke. 

Q.       Why  do  LAMPS  SMOKE  ? 

A.  Either  because  the  wick  is  cut 
unevenly,  or  else  because  it  is  turned  up 
too  high. 

4* 


82  CHEMICAL    ACTION. 

Q.       Why  does  a  LAMP  SMOKE  when  the  WICK  is 

Wbt  UNEVENLY  ? 

A.  1st — Because  the  points  of  the 
jagged  edge  (being1  very  easily  separated 
from  the  wick)  load  the  flame  with  more 
carbon  than  it  can  consume  ;  and 

2dly — As  the  heat  of  the  flame  is 
greatly  diminished  by  these  bits  of  wick, 
at  is  unable  to  consume  even  the  usual 
^quantity  of  smoke. 

Q.  Why  does  a  LAMP  SMOKE  when  the  WICK  is 
turned  up  too  HIGH? 

A.  Because  more  carbon  is  separated 
from  the  wick  than  can  be  consumed  by 
.the  flame. 

Q.       Why  do  not  "  ARGAND  BURNERS  "  smoke  ? 

A.  Because  a  current  of  air  passes 
through  the  middle  of  the  flame ;  in  con- 
sequence of  which,  the  carbon  of  the 
interior  is  consumed,  as  well  as  that  in 
•the  outer  coating  of  the  flame. 

Q.  Why  does  a  LAMP-GLASS  DIMINISH  the 
SMOKE  of  a  lamp? 

A.  1st — Because  it  increases  the 
supply  of  oxygen  to  the  flame,  by  produ- 
cing* a  draught ;  and 

2dly — It  concentrates  and  reflects  the 
heat  of  the  flame ;  in  consequence  of 
which,  the  combustion  of  the  carbon  is 


ANIMAL    HEAT.  83 

more  perfect,    and   very   little   escapes 
unconsumed. 


CHAPTER  VII. 

AIWMAL   HEAT. 

Q.       What  is  the  cause  of  ANIMAL  HEAT  ? 

A.  Animal  heat  is  produced  by  the 
combustion  of  hydrogen  and  carbon  in 
the  capillary  vessels. 

Q.       What  are  CAPILLARY  VESSELS  ? 

A.  Vessels  as  small  as  hairs  running* 
all  over  the  body  ;  they  are  called  capil- 
lary from  the  Latin  word  "  capilla  ris" 
(like  a  hair}. 

Q.  Do  these  CAPILLARY  VESSELS  run  all  over 
the  human  body  ? 

A.  Yes.  Whenever  blood  flows  from 
a  wound,  some  vein  or  vessel  must  be 
divided  ;  and  as  you  can  bring"  blood 
from  any  part  of  the  body  by  a  very 
slight  wound,  these  little  vessels  must 
run  through  every  part  of  the  human 
frame. 

Q.  How  do  HYDROGEN  gas  and  CARBON  get 
into  these  very  little  vessels  ? 

A.     The  food  we  eat  is  converted  into 


84  CHEMICAL    ACTION. 

blood ;  and  blood  contains  both  hydrogen 
and  carbon. 

Q.  How  does  COMBUSTION  take  place  in  the  car 
pillary  vessels  ? 

A.  The  carbon  of  the  blood  combines 
with  oxygen  of  the  air  we  breathe,  and 
forms  into  carbonic  acid  gas. 

Q.  What  BECOMES  of  this  CARBONIC  ACID  GAS 
formed  in  the  human  blood  ? 

A.  The  lungs  throw  off  almost  all  of 
it  into  the  air,  by  the  act  of  respiration. 

Q.  What  GAS  is  generated  in  a  common  FIRE 
by  COMBUSTION? 

A.  Carbonic  acid  gas — formed  by  the 
union  of  the  carbon  of  fuel  with  the  oxy- 
gen of  the  air. 

Q.  What  GAS  is  generated  by  a  lighted  CANDLE 
or  LAMP  ? 

A.  Carbonic  acid  gas — formed  by 
the  union  of  the  carbon  of  the  oil  or  tal- 
low with  the  oxygen  of  the  air. 

Q.  What  is  the  cause  of  SPONTANEOUS  COM- 
BUSTION? 

A.  The  piled-up  goods  ferment  from 
heat  and  damp  ;  and  (during  fermenta- 
tion) carbonic  acid  gas  is  formed^  which  is 
attended  with  combustion. 

Q.  Does  the  HEAT  of  the  HUMAN  BODY  arise  from 
the  SAME  CAUSE  as  the  heat  of  FIRE  ? 

A.     Yes,  precisely.     The   carbon  of 


ANIMAL    HEAT.  85 

the  blood  combines  with  the  oxygen  of  the 
air  inhaled,  and  produces  carbonic  acid 
gas,  which  is  attended  with  combustion. 

Q.  If  animal  heat  is  produced  by  COMBUSTION, 
why  does  not  the  human  body  BURN  UP  like  a  coal  or 
candle  ? 

A.  It  actually  does  so.  Every  mus- 
cle, nerve,  and  organ  of  the  body,  actu- 
ally wastes  away  like  a  burning  candle ; 
and  (being*  reduced  to  air  and  ashes)  is 
rejected  from  the  system  as  useless. 

Q.  If  every  bone,  muscle,  nerve,  and  organ,  is 
thus  consumed  by  combustion,  why  is  not  the  BODY 
entirely  CONSUMED  ? 

A.  It  would  be  so,  unless  the  parts 
destroyed  icere  perpetually  renewed:  but 
as  a  lamp  will  not  go  out,  so  long1  as  it 
is  supplied  with  fresh  oil — neither  will 
the  body  be  consumed,  so  long-  as  it  is 
supplied  with  sufficient  food. 

Q.  What  is  the  principal  DIFFERENCE  between 
the  combustion  of  a  FIRE  or  LAMP  and  that  of  the 

HUMAN  BODY  ? 

A.  In  the  human  body,  the  combus- 
tion is  effected  at  a  much  lower  temper- 
ature;  and  is  carried  on  more  slowly, 
than  it  is  in  a  lamp  or  fire. 

Q.  How  is  it  that  carbon  can  be  made  to  burn 
at  so  LOW  a  temperature  in  the  human  body  ? 

A.     Because  the  carbon  in  the  blood 


86  CHEMICAL    ACTION. 

is  reduced  to  very  minute  particles  ;  and 
these  particles  are  ready 'to  undergo  a 
rapid  change  as  soon  as  oxygen  is 
supplied. 

Q.  WTien  a  man  is  STARVED,  what  parts  of  the 
body  go  first  ? 

A.  First  the  fat}  because  it  is  the 
most  combustible ;  then  the  muscles ; 
last  of  all  the  brain ;  and  then  the  man 
dies,  like  a  candle  which  is  burnt  out. 

Q.  Why  does  WANT  of  sufficient  NOURISHMENT 
often  produce  MADNESS  ? 

A.  Because  after  the  fat  and  muscles 
of  the  body  have  been  consumed  by  ani- 
mal combustion,  the  brain  is  next  attack- 
ed ;  and  (unless  the  patient  dies)  mad- 
ness  ensues. 

Q.       Why  does  a  man  SHRINK  when  STARVED  ? 

A.  Because  the  capillary  fires  feed 
upon  the  human  body  when  they  are  not 
supplied  with  food-fuel.  A  starved  man 
shrinks  just  as  a  fire  does,  when  it  is  not 
supplied  with  fuel. 

Q.       What  is  the  FUEL  of  the  BODY  ? 

A.  Food  is  the  fuel  of  the  body. 
The  carbon  of  the  food  mixing  with  the 
oxygen  of  the  air,  evolves  heat  in  the 
same  way  that  a  fire  or  candle  does. 

Q.       Why  is  EVERY  part  of  the  BODY  WARM? 


ANIMAL    HEAT.  87 

A.  Because  the  capillary  vessels  run 
through  every  part  of  the  human  body, 
and  the  combustion  of  blood  takes  place 
in  the  capillary  vessels. 

See  p.  84. 

Q.       Why  does  RUNNING  make  us  WARM  ? 

A.  Because  we  inhale  air  more  ra- 
pidly when  we  run,  and  cause  the  blood 
to  pass  more  rapidly  through  the  lungs 
in  contact  with  it.  Running  acts  upon 
the  capillary  vessels  as  a  pair  of  bellows 
on  a  common  fire. 

Q.  Why  does  INHALING  AIR  RAPIDLY  make  the, 
body  feel  WARM  ? 

A.  Because  more  oxygen  is  intro- 
duced into  the  body.  In  consequence 
of  which,  the  combustion  of  the  blood  is 
more  rapid — the  blood  itself  more  heated 
— and  every  part  of  the  body  is  made 
warmer. 

Q,       Why  does  HARD  WORK  produce  HUNGER  ? 

A.  Because  it  produces  quicker  respi- 
ration ;  by  which  means,  a  larger  amount 
of  oxygen  is  introduced  info  the  lungs, 
and  the  capillary  combustion  increased. 
Hunger  is  the  notice  (given  by  our  body) 
to  remind  us  that  our  food-fuel  must  be 
replenished. 

Q.       Why  does  SINGING  make  us  HUNGRY  ? 


88  CHEMICAL    ACTION. 

A.  Because  it  increases  respiration  ; 
and,  as  more  oxygen  is  introduced  into 
the  lung-s,  our  food-fuel  is  more  rapidly 
consumed. 

Q.       Why  does  READING  ALOUD  make  us  feel 

HUNGRY  ? 

A.  Because  it  increases  respiration; 
and,  as  more  oxygen  is  introduced  into 
the  lungs,  our  foodrfael  is  more  rapidly 
consumed. 

Q.  Why  do  we  feel  less  HUNGRY  in  the  night 
than  in  the  DAY  ? 

A.  Because  we  breathe  more  slowly 
during  sleep ;  therefore,  less  oxygen  is 
introduced  into  the  lung's,  to  consume  our 
food-fuel. 

Q.  Why  do  we  need  WARMER  CLOTHING  by 
NIGHT  than  by  DAY  ? 

A.  1st — Because  the  night  is  gener- 
ally colder  than  the  day  ;  and 

2dly — Our  bodies  are  colder  also  ;  be- 
cause we  breathe  more  slowly,  and  our 
animal  combustion  is  retarded. 

Q.       Why  do  we  PERSPIRE  when  very  hot  ? 

A.  The  pores  of  the  body  are  like  the 
safely  valves  of  a  steam-engine  ;  when 
the  heat  of  the  body  is  very  great,  some 
of  the  combustible  matter  of  the  blood 
is  thrown  off  in  perspiration;  and  the 
heat  of  the  body  kept  more  temperate. 


ANIMAL    HEAT.  89 

Q.  Why  do  persons  feel  LAZY  and  averse  to 
exercise  when  they  are  HALF-STARVED  or  ILL-FED? 

A.  Animal  food  contains  great  nou- 
rishment, and  produces  a  desire  for  active 
occupations ;  but,  when  the  body  is  not 
supplied  with  strong  food,  this  desire 
for  muscular  action  ceases,  and  the  person 
grows  slothful. 

Q.  Why  have  persons  who  follow  HARD,  OUT- 
OF-DOORS  OCCUPATIONS  more  APPETITE  than  those 
who  are  engaged  in  SEDENTARY  pursuits  ? 

A.  Hard  bodily  labor  in  the  open  air 
causes  much  oxygen  to  be  conveyed  into 
the  lungs  by  inspiration ;  the  combustion 
of  the  food  is  carried  on  quickly  ;  animal 
heat  increased;  and  need  for  nutritious 
food  more  quickly  indicated  by  craving 
hunger. 

Q.  Why  have  persons  who  follow  SEDENTARY 
PURSUITS  less  APPETITE  than  ploughmen  and  masons? 

A.  1st — Because  the  air  they  inhale 
is  less  pure,  being  deprived  of  some  of 
its  oxygen :  and 

A.  2dly — Their  respiration  is  neither 
so  quick,  nor  so  strong ;  and,  therefore, 
the  combustion  of  their  food  is  carried  on 
more  slowly. 

Q.  Why  do  we  like  strong  MEAT  and  GREASY 
food  when  the  WEATHER  is  very  COLD  ? 

A.     Because  strong  meat  and  grease 


90  CHEMICAL    ACTION. 

contain  large  portions  of  carbon  and  hy- 
drogen; which  (when  burned  in  the 
blood)  produce  a  larger  amount  of  heat, 
than  any  other  kind  of  food. 

Q.  Why  do  persons  EAT  MORE  food  in  COLD 
weather  than  in  hot  ? 

A.  Because  the  body  requires  more 
fuel  in  cold  weather p,  to  keep  up  the  same 
amount  of  animal  tieat ;  and  as  wre  put 
more  coals  on  a  fire  on  a  cold  day,  to  keep 
our  room  warm  ;  so  we  eat  more  food 
on  a  cold  day,  to  keep  our  body  warm. 

Q.       Why  does  COLD  produce  HUNGER  ? 

A.  1st  —  Because  the  air  contains 
more  oxygen  in  cold  weather;  and,  there- 
fore, fires  burn  more  fiercely,  and  animal 
combustion  is  more  rapid :  and 

2dly — As  we  are  more  active  in  cold 
weather,  our  increased  respiration  acts 
like  a  pair  of  bellows  on  the  capillary 
combustion. 

Q.  Why  does  rapid  DIGESTION  produce  a  cra- 
ving APPETITE? 

A.  This  is  a  wise  providence  to  keep 
our  bodies  in  health  ;  they  give  notice  (by 
hunger)  that  the  capillary  jires  need  re- 
plenishing, in  order  that  the  body  itself 
may  not  be  consumed. 

Q.  Why  do  we  feel  a  desire  for  ACTIVITY  in 
cold  weather  ? 


ANIMAL    HEAT.  91 

A.  1st — Because  activity  increases 
the  warmth  of  the  body,  by  fanning  the 
combustion  of  the  blood :  and 

2dly — The  strong  food  we  eat  creates 
a  desire  for  muscular  exertion. 

Q.  Why  are  the  Esquimaux  so  passionately 
fond  of  TRAIN  OIL  and  WHALE  BLUBBER  ? 

A.  Because  oil  and  blubber  contain 
large  quantities  of  carbon  and  hydrogen, 
which  are  exceedingly  combustible ; 
and,  as  these  people  live  in  climates  of 
intense  cold,  the  heat  of  their  bodies  is 
increased  by  the  greasy  nature  of  their 
food. 

Q.  Why  do  we  feel  a  DISLIKE  to  strong  meat 
and  greasy  food  in  very  HOT  weather  ? 

A.  Because  strong1  meat  and  grease 
contain  so  much  carbon  and  hydrogen, 
that  they  would  make  us  intensely  hot : 
we  therefore,  instinctively  refuse  them  in 
hot  weather. 

Q.  Why  -do  we  like  FRUITS  and  VEGETABLES 
most  in  hot  weather  ? 

A.  Because  they  contain  less  hydro- 
gen and  carbon  than  meat;  and,  there- 
fore, produce  both  less  blood,  and  blood 
of  a  less  combustible  nature. 

Q.  Why  is  the  blood  of  a  less  COMBUSTIBLE  na- 
ture, if  we  live  chiefly  upon  FRUITS  and  VEGETABLES  ? 

A.     Because    fruits    and   vegetables 


92  CHEMICAL    ACTION. 

supply  the  blood  with  a  very  large 
amount  of  water ;  which  is  not  combusti- 
ble, like  the  carbon  and  hydrogen  of 
strong*  meat. 

Q.  How  do  FRUITS  and  VEGETABLES  COOL  the 
BLOOD? 

A.  1st — They  diminish  the  amount  of 
carbon  and  liydrogen  in  the  blood,  which 
are  the  chief  causes  of  animal  heat :  and 

2dly — They  supply  the  blood  with  a 
large  amount  of  water,  which  exudes 
through  the  skin,  and  leaves  the  body 
cool. 

Q.  Why  do  ice  feel  LAZY  and  averse  to  activity 
in  very  HOT  WEATHER  ? 

A.  1st — Because  muscular  activity 
increases  the  heat  of  the  body,  by  quick- 
ening the  respiration :  and 

2dly — The  food  we  eat  in  hot  wea- 
ther (not  being-  greasy}  naturally  abates 
our  desire  for  bodily  activity. 

Q.  .  Why  do  the  inhabitants  of  TROPICAL  coun- 
tries live  chiefly  upon  RICE  and  FRUIT? 

A.  Because  rice  and  fruit  (by  diges- 
tion) are  mainly  converted  into  ivater  ;  and 
(by  cooling  the  blood)  prevent  the  tropical 
heat  from  feeling  so  oppressive. 

Q.       Why  are  the  ILL-FED  instinctively  AVERSE 

tO  CLEANLINESS? 


ANIMAL    HEAT.  93 


A.  Because  cleanliness  increases  hun- 
ger,  which  they  cannot  allay  by  food. 

Q.  Why  are  the  ILL-CLAD  also  instinctively 
averse  to  CLEANLINESS  ? 

A.  Because  dirt  is  warm,  (thus  pigs, 
who  love  warmth)  are  fond  of  dirt) ;  to 
those,  therefore,  who  are  very  ill-dad, 
the  warmth  of  dirt  is  agreeable. 

Q.       Why  are  very  POOR  PEOPLE  instinctively 

AVERSE  to  VENTILATION  ? 

A.  1st — Because  ventilation  increases 
the  oxygen  of  the  air — the  combustion  of 
food — and  the  cravings  of  appetite  :  and 

2dly — Ventilation  cools  the  air  of  our 
rooms :  to  poor  people,  therefore,  who  are 
ill-clad,  the  warmth  of  an  ill-ventilated 
apartment  is  agreeable. 

Q.       Why  does  FLANNEL,  <^c.,  make  us  WARM  ? 

A.  Flannel  and  warm  clothing  do 
not  make  us  warm,  but  merely  prevent 
our  body  from  becoming  cold. 

Q.  How  does  FLANNEL,  <^c.,  prevent  our  body 
from  becoming  cold  ? 

A.  Flannel  (being  a  bad  conductor) 
will  neither  carry  off  the  heat  of  our  body 
into  the  cold  air,  nor  suffer  the  cold  of 
the  air  to  come  in  contact  with  our  ivarm 
body :  arid  thus  it  is,  that  flannel  clothing 
keeps  us  warm. 


94  MECHANICAL   ACTION. 

Q.  WJiy  are  FROGS  and  FISHES  COLD-BLOODED 
animals  ? 

A.  Because  they  consume  very  little 
air ;  and,  without  a  plentiful  supply  of 
air.  combustion  is  too  slow  to  generate 
much  animal  heat. 

Q.       Why  is  a  DEAD  BODY  COLD  ? 

A.  Because  air  is  no  longer  conveyed 
to  the  lungs,  after  respiration  has  ceased ; 
and,  therefore,  animal  heat  is  no  longer 
generated  by  combustion. 


MECHANICAL    ACTION. 

CHAPTER  VIIL 

1. — PERCUSSION. 

Q.  How  is  heat  produced  by  MECHANICAL  AC- 
TION 1 

A.  1. — By  Percussion.  2. — By  Fric- 
tion. And  3. — By  Condensation. 

Q.       What  is  meant  by  PERCUSSION  ? 

A.  The  act  of  striking ;  as  when  a 
blacksmith  strikes  a  piece  of  iron  on  his 
anvil  with  his  hammer. 

Q.       Why  does  STRIKING  IRON  make  it  RED  HOT  ? 

A.     Because  it  condenses  the  particles 


PERCUSSION.  95 

of  the  metal,  and  makes  the  latent  heat 
sensible. 

Q.       Does  COLD  iron  contain  HEAT  ? 

A.  Yes ;  everything  contains  heat ; 
but,  when  a  thing-  feels  cold,  its  heat  is 

LATENT. 

Q.       What  is  meant  by  LATENT  HEAT  ? 

A.  Heat  not  perceptible  to  our  feelings. 
When  anything  contains  heat  without 
feeling  the  hotter  for  it,  that  heat  is 
called  "  latent  heat." 

See  p.  37. 
Q.       Does  COLD  iron  contain  latent  HEAT  ? 

A.  Yes ;  and  when  a  blacksmith 
compresses  the  particles  of  iron  by  his 
hammer,  he  brings  out  latent  heat ;  and 
this  makes  the  iron  red  hot. 

Q.  How  used  blacksmiths  to  LIGHT  THEIR 
MATCHES  before  the  general  use  of  lucifers  ? 

A.  They  used  to  place  a  soft  iron 
nail  upon  their  anvil ;  strike  it  two  or 
three  times  with  a  hammer;  and  the 
point  became  sufficiently  hot  to  light  a 
brimstone  match. 

Q.  How  can  a  NAIL  (beaten  by  a  hammer) 
IGNITE  a  brimstone  MATCH  ? 

A.  The  particles  of  the  nail  being 
compressed  by  the  hammer,  can  no  longer 
contain  so  much  heat  in  a  latent  state,  as 


96  MECHANICAL    ACTION. 

they  did  before;  some  of  it,  therefore, 
becomes  sensible,  and  increases  the  tem- 
perature of  the  iron. 

Q.  Why  does  STRIKING  a  FLINT  against  a 
piece  of  STEEL  produce  a  SPARK  ? 

A.  Because  it  compresses  those  parts 
of  the  flint  and  steel  which  strike  toge- 
tlier.  In  consequence  of  which,  some  of 
their  latent  heat  is  disturbed,  and  exhi- 
bits itself  in  a  spark. 

Q.  How  does  this  development  of  HEAT  produce 
a  SPARK  and  set  TINDER  on  fire? 

A.  A  very  small  fragment  (either  of 
the  steel  or  flint)  is  knocked  off  red  hot, 
and  sets  fire  to  the  tinder  on  which  it 
falls. 

Q.  Why  is  it  needful  to  keep  BLOWING  the 
TINDER  with  the  breath  ? 

A.  In  order  that  the  increased  sup- 
ply of  air  may  furnish  the  tinder  with 
more  oxygen  to  assist  combustion. 

Q.  Where  does  the  OXYGEN  of  the,  air  'COME 
FROM,  which  is  blown  to  the  lighted  tinder  ? 

A.  From  the  air  itself,  which  is  com- 
posed of  two  gases  (nitrogen  and  oxygen) 
mixed  together. 

Every  5  gallons  of  common  air  contain  nearly  4  gallons 
of  nitrogen,  and  1  of  oxygen. 

Q.  What  is  the  USE  of  OXYGEN  GAS  to  lighted 
tinder  ? 


FRICTION.  97 

A.  It  supports  tlw  combustion  of  the 
tinder.  Blowing  lighted  tinder  carries 
oxygen  to  it  and  quickens  it,  in  the  same 
way  as  a  pair  of  bellows  quickens  a  dull 
fire. 

Q.  Why  do  HORSES  sometimes  STRIKE  FIRE 
with  their  FEET  ? 

A.  Because  when  their  iron  shoes 
strike  against  the  flint  stones  of  the  road, 
very  small  fragments  (either  of  the  shoe 
or  stones)  are  knocked  off  red  hot,  and 
look  like  sparks. 

Q.       WTiat  makes  these  fragments  RED  HOT? 

A.  The  percussion  condenses  the  part 
struck :  In  consequence  of  which,  some 
of  its  latent  heat  is  rendered  sensible,  and 
exhibits  itself  in  these  red  hot  fragments. 


CHAPTER  IX. 
2. — FRICTION. 

Q.       What  is  meant  by  FRICTION  ? 

A.  The  act  of  rubbing  two  things  to- 
gether ;  as  the  Indians  rub  two  pieces  of 
wood  together  to  produce  fire. 

Q.      How  do  the  Indians  produce  FIRE  by  merely 

RUBBING  TWO  PIECES  of  dry  WOOD  TOGETHER? 

5 


98 


MECHANICAL    ACTION. 


A.  They  take  a  piece  of  dry  wood, 
sharpened  to  a  point,  which  they  rub 
quickly  up  and  down  a  flat  piece,  till  a 
groove  is  made  ;  and  the  dust  (collected 
in  this  groove)  catches  fire. 

Q.       Why  does  the  dust  of  the  WOOD  CATCH  FIRE 

by  RUBBING  ? 

A.  Because  latent  heat  is  developed 
from  the  wood  by  friction. 

The  best  woods  for  this  purpose  are  boxwood  against 
mulberry,  or  laurel  against  poplar  or  ivy. 

Q.  Do  not  CARRIAGE  WHEELS  SOmetWUS  CATCH 
FIRE? 

A.  Yes  ;  when  the  wheels  are  dry — 
or  fit  too  tightly — or  revolve  very  rapidly. 

Q.       Why  do  wheels  catch  fire  in  such  cases  ? 

A.  Because  the  friction  of  the  wheels 
against  the  axle-tree  disturbs  their  latent 
heat,  and  produces  ignition. 

Q.       What  is  the  use  of  GREASING  CART  WHEELS  ? 

A.  Grease  lessens  the  friction ;  and, 
because  there  is  less  friction,  the  latent 
heat  of  the  wheels  is  less  disturbed. 

Q.  WTty  does  RUBBING  our  HANDS  and  FACES 
make  them  feel  WARM? 

A.  1st — Because  friction  excites  the 
latent  heat  of  our  hands  and  faces,  and 
makes  it  sensible  to  our  feeling  :  and 

2dly — The  blood  is  made  to  circulate 
more  quickly  ;  in  consequence  of  which, 


FRICTION.  99 

the  quantum  of  heat  (left  in  its  passage) 
is  increased. 

Q.  When  a  man  has  been  almost  DROWNED, 
why  is  suspended  animation  RESTORED  by  RUBBING  1 

A.  1st — Because  friction  excites  the 
latent  heat  of  the  half-inanimate  body : 
and 

2dly — It  makes  the  blood  circulate 
more  quickly,  which  increases  the  animal 
heat. 

Q.  Why  do  two  pieces  of  ICE  (rubbed  together) 
MELT? 

A.  Ice  contains  140  degrees  of  latent 
Iwat,  and  (when  two  pieces  are  rubbed 
together)  some  of  this  latent  heat  is  made 
sensible,  and  melts  the  ice. 

Q.  Are  not  FORESTS  sometimes  SET  on  FIRE  by 
friction  ? 

A.  Yes ;  when  two  branches  or 
trunks  of  trees  (blown  about  by  the 
wind)  rub  violently  against  each  other , 
their  latent  heat  is  developed,  and  sets  fire 
to  the  forests. 

Q.  Why  do  carpenters1  TOOLS  (such  as  gimlets, 
saws,  files,  fyc.)  become  HOT  when  used  ? 

A.  Because  the  friction  of  the  tools 
against  the  wood  disturbs  its  latent  heat, 
and  makes  it  sensible. 

Q.       Give  an  ILLUSTRATION  of  this. 

A.     When  cannon  is  bored,  the  borers 


100  MECHANICAL    ACTION. 

become  so  intensely  hot  from  friction,  that 
they  would  blister  the  hands,  if  touched. 

Q.  Why  do  these  BORERS  become  so  i?ite?iscly 
HOT? 

A.  Because  the  friction  of  the  borers 
ag-ainst  the  metal  is  so  great,  that  it  sets 
free  a  large  quantity  of  latent  heat. 


CHAPTER  X. 
3. — CONDENSATION  or  COMPRESSION.* 

Q.       What  is  meant  by  COMPRESSION  ? 

A.  The  act  of  bringing  parts  nearer 
together  ;  as  a  spong*e  is  compressed  by  be- 
ing* squeezed  in  the  hand. 

Q.  Cannot  HEAT  be  evolved  from  common  air 
merely  by  COMPRESSION  ? 

A.  Yes  ;  if  a  piece  of  German  tinder 
be  placed  at  the  bottom  of  a  glass  tube, 
and  the  air  in  the  tube  compressed  by 
a  piston,  the  tinder  will  catch  fire. 

In  a  common  syringe  or  squirt,  the  Handle  part  (which 
contains  the  sucker,  and  is  forced  up  and  down)  is  called 
"  the  Piston." 

*  N.  B.  The  reduction  of  matter  into  a  smaller  com- 
pass by  any  external  or  mechanical  force  is  called  COM- 
PRESSION. 

The  reduction  of  matter  into  a  smaller  compass  by  some 
internal  action  (as  by  the  escape  of  caloric)  is  called  CON- 
DENSATION. 


CONDENSATION    OR    COMPRESSION.      101 

Q.       Why  will  the  tinder  catch  fire  ?       , 

A.  Because  the  air  is  compressed, 
and  its  latent  heat  being  squeezed  out-, 
sets  fire  to  the  tinder  at  the  bottom  of 
the  tube. 

Q.  When  an  AIR-GUN  is  discharged  in  the 
dark,  why  is  it  accompanied  with  a  slight  FLASH  ? 

A.  Because  the  air  is  very  rapidly 
condensedj  and  its  latent  heat  developed 
in  a  flash  of  light. 

N.  B.  If  a  glass  lens  be  fixed  in  the  copper  ball,  (where 
the  air  of  the  gun  is  condensed?)  a  flash  of  light  may  be 
distinctly  discerned  at  the  stroke  of  the  piston. 

Q.  Why  do  DETONATING  salt  and  powder  EX- 
PLODE on  being  rubbed  or  struck  ? 

A.  Because  the  mechanical  action  of 
rubbing-  or  striking,  produces  sufficient 
heat  to  ignite  the  explosive  materials  of 
which  they  are  composed. 

Q.  Why  are  SHOT  and  CANNON-BALLS  HEATED 
by  being  discharged  from  a  gun  or  cannon  ? 

A.  Because  the  air  is  so  rapidly  con- 
densed, when  the  discharge  is  made,  that 
sufficient  latent  heat  is  developed  to 
make  the  shot  or  balls  hot. 

Q.  Why  does  the  HOLE  made  by  a  shot  or  can- 
non-ball  in  a  wall  or  timber,  look  as  if  it  were  BURNT  ? 

A.  Because  the  shot  or  cannon-balls 
were  so  heated  by  the  discharge,  as  ac- 
tually to  scorch  the  material  into  which 
they  penetrated. 


102  EFFECTS    OF    HEAT. 

EFFECTS    OF    HEAT. 

CHAPTER    XL 
1. — EXPANSION. 

Q.       What  are  the  principal  EFFECTS  of  HEAT  ? 

A.  1. — Expansion.  2.  —  Liquefac- 
tion. 3. — Vaporization.  4. — Evapora- 
tion ;  and  5. — Ignition. 

Q.         DOES  HEAT  EXPAND  AIR  'I 

A.  Yes ;  if  a  bladder  (partially  filled 
with  air)  be  tied  up  at  the  neck,  and  laid 
before  the  fire,  the  air  will  expand  till  the 
bladder  bursts. 

Q.  Why  will  the  AIR  SWELL  if  the  bladder  be 
laid  before  the  fire? 

A.  Because  the  heat  of  the  fire  will 
drive  the  particles  of  air  apart  from  each 
other,  and  cause  them  to  occupy  more 
room  than  they  did  before. 

Q.  Why  do  unslit  CHESTNUTS  CRACK  with  a 
loud  noise  when  ROASTED  ? 

A.  Because  they  contain  a  great  deal 
of  air  which  is  expanded  by  the  heat  of 
the  fire ;  and  not  being  able  to  escape, 
bursts  violently  through  the  thick  rind, 
slitting  it)  and  making  a  great  noise. 


EXPANSION.  103 

Q.  What  occasions  the  loud  CRACK  or  report 
which  we  hear  ? 

A.  1st — The  sudden  bursting  of  the 
rind  makes  a  report ;  in  the  same  way 
as  a  piece  of  wood  or  glass  would  do,  if 
snapped  in  two :  and 

2dly — The  escape  of  hot  air  from  the 
chestnut  makes  a  report  also ;  in  the 
same  way  as  gunpowder,  when  it  escapes 
from  a  gun. 

Q.  Why  does  the  sudden  BURSTING  of  the  rind^ 
or  SNAPPING  of  a  piece  of  wood,  make  a  REPORT  ? 

A.  Because  a  violent  jerk  is  given 
to  the  air,  when  the  attraction  of  cohe- 
sion is  thus  suddenly  overcome.  This 
jerk  produces  rapid  undulations  in  the 
air,  which  (striking*  upon  the  ear)  give 
the  brain  a  sensation  of  sound. 

Q.  Why  does  the  ESCAPE  of  AIR  from  the  chest- 
nut,  or  the  EXPLOSION  of  GUNPOWDER,  produce  a 
REPORT? 

A.  Because  the  sudden  expansion  of 
the  imprisoned  air  produces  a  partial 
vacuum ;  the  report  is  caused  by  the 
rushing  of  fresh  air  to  fill  up  this  vacuum. 

See  Thunder,  p.  15. 

Q.  If  a,  CHESTNUT  be  SLIT,  it  will  NOT  CRACK  ; 
why  is  this  ? 

A.     Because   the   heated  air  of  the 


104  EFFECTS    OF    HEAT. 

chestnut  can  then  freely  escape  through 
the  slit  in  the  rind. 

Q.  Why  does  an  APPLE  split  and  SPURT  about 
when  roasted? 

A.  Because  it  contains  a  vast  quanti- 
ty of  air,  which  (being  expanded  by  the 
heat  of  the  fire)  bursts  through  the  peel, 
carrying  the  juice  of  the  apple  along 
with  it. 

Q  Does  an  APPLE  contain  MORE  AIR  in  'propor- 
tion than  a  CHESTNUT  1 

A.  Yes,  much  more.  There  is  as 
much  condensed  air  in  a  common  apple, 
as  would  fill  a  space  48  times  as  large 
as  the  apple  itself. 

Q.      How  can  all  this  AIR  %e  stowed  in  an  APPLE  ? 

A.  The  inside  of  an  apple  consists  of 
little  cells  (like  a  honey-comb),  each  of 
which  contains  a  portion  of  the  air. 

Q.  When  an  APPLE  is  ROASTED,  why  is  one 
part  made  SOFT,  while  all  the  rest  remains  hard  ? 

A.  Because  the  air  in  those  cells  next 
the  Jire  is  expanded,  and  flies  out ;  the 
cells  are  broken,  and  their  juices  mixed 
together;  so  the  apple  collapses  (from  loss 
of  air  arid  juice),  and  feels  soft  in  those 
parts. 

Q.       IVTiat  is  meant  by  the  "  apple  COLLAPSING?" 

A.     It  means  that  the  plumpness  gives 


EXPANSION.  105 

way,  and  the  apple  becomes  flabby  and 
shrivelled. 

Q.  Why  do  SPARKS  of  fire  start  (with  a  crack- 
ling noise)  from  pieces  of  WOOD  laid  upon  a  FIRE  ? 

A.  Because  the  air  (expanded  by 
the  heat)/orces  its  way  through  the  pores 
of  the  wood;  and  carries  along1  with  it 
the  covering  of  the  pore,  which  resisted 
its  passage. 

Q.       What  is  meant  by  the  "  PORES  of  the  WOOD  ?" 
A.     Very   small    holes   in  the  wood, 
through  which  the  sap  circulates. 

Q.  What  are  the  SPARKS  OF  FIRE  which  burst 
from  the  WOOD  ? 

A.  Very  small  pieces  of  wood  made 
red  hat,  and  separated  from  the  log-  by 
the  force  of  the  air,  when  it  bursts  from 
its  confinement. 

Q.  Why  does  DRY  PINE  make  more  snapping 
than  any  OTHER  WOOD  ? 

A.  Because  the  pores  of  pine  are  very 
large,  and  contain  more  air  than  wood 
of  a  closer  grain. 

Q.  Why  does  GREEN  WOOD  make  LESS  SNAP- 
PING than  DRY  ? 

A.  Because  the  pores  being*  filled 
with  sap,  contain  very  little  air. 

Q.  Why  does  DRY  WOOD  make  MORE  SNAPPING 
than  green  ? 

5* 


106  EFFECTS    OF    HEAT. 

A.  Because  the  sap  is  dried  up,  and 
the  pores  are  filled  with  air  instead. 

Q.  Why  does  DRY  wood  BURN  more  easily  than 
GREEN  or  wet  wood  ? 

A.  Because  the  pores  of  dry  wood 
are  filled  with  air  which  supports  com- 
bustion ;  but  the  pores  of  green  or  wet 
wood  are  filled  with  moisture,  which  ex- 
tinguishes flame. 

Q.       Why  does  MOISTURE  EXTINGUISH  FLAME  ? 

A.  1st — Because  it  prevents  the  hy- 
drogen of  the  fuel  from  mixing1  with  the 
oxygen  of  the  air,  to  form  carbonic  acid 
gas;  and 

2dly — Because  heat  is  perpetually 
carried  off,  by  the  formation  of  the  sap 
or  moisture  into  steam. 

Q.  Why  do  STONES  SNAP  and  fly  about  when 
heated  in  the  FIRE  ? 

A.  Because  the  close  texture  of  the 
stone  prevents  the  hot  air  from  escaping- ; 
in  consequence  of  which,  it  bursts  forth 
ivith  great  violence,  tearing*  the  stone  to 
atoms,  and  forcing-  the  frag-ments  into 
the  room. 

Probably  some  part  of  this  effect  is  due  to  the  setting 
free  of  the  water  of  crystallization. 

Q.  Wh.en  bottled  ALE  or  PORTER  is  set  before  a 
PIRE,  why  is  the  CORK  FORCED  OUT  sometimes  ? 

A.     Because  the  carbonic  acid  of  the 


EXPANSION.  107 

liquor  expands  by  the  heat,  and  drives 
out  the  cork. 

Carbonic  acid  gas  is  a  compound  of  carbon  and  oxygen. 
The  carbon  comes  from  the  fuel,  and  the  oxygen  from  the 
air.  See  p.  40. 

Q.  Why  does  ALE  or  PORTER  FROTH  more  after 
it  has  been  set  before  the  fire'} 

A.  Because  the  heat  of  the  fire  sets 
free  the  carbonic  acid  of  the  liquor ; 
which  is  entangled  as  it  rises  through 
the  liquor,  and  produces  bubbles  or  froth. 

Q.  When  a  boy  makes  a  BALLOON,  and  sets 
fire  to  the  cotton  or  sponge  (which  has  been  steeped  in 
spirits  of  wine),  why  is  the  balloon  INFLATED? 

A.  Because  the  air  of  the  balloon  is 
expanded  by  the  flame,  till  every  crumple 
is  inflated  and  made  smooth. 

Q.  Why  does  the  BALLOON  RISE  after  it  has 
been  inflated  by  the  expanded  air  ? 

A.  Because  the  same  quantity  of  air 
is  expanded  to  three  or  four  times  its  ori- 
ginal volume;  and  made  so  much  lighter, 
that  even  when  all  the  paper,  wire,  and 
cotton  are  added,  it  is  still  lighter  than 
common  air. 

Q.       Why  does  SMOKE  RUSH  UP  a  CHIMNEY  ? 

A.  Because  the  heat  of  the  fire  ex- 
pands the  air  in  the  chimney;  which 
(being-  thus  made  lighter  than  the  air 
around)  rises  up  the  chimney,  and  carries 
the  smoke  in  its  current. 


108  EFFECTS    OF    HEAT. 

Q.  Why  will  a  LONG  chimney  SMOKE,  unless 
the  FIRE  be  pretty  FIERCE? 

A.  Because  the  heat  of  the  fire  will 
not  be  sufficient  to  rarefy  all  the  air  in 
the  chimney. 

Q.  WHY  will  the  chimney  smoke,  unless  the  fire 
be  FIERCE  enough  to  heat  ALL  the  air  in  the  CHIMNEY 
FLUE? 

A.  Because  the  cold  air  ("condensed 
in  the  upper  part  of  the  flue)  will  sink 
from,  its  own  weight ;  and  sweep  the  as- 
cending1 smoke  back  into  the  room. 

Q.  What  is  the  use  of  a  COWL  upon  a  chim- 
ney-pot ? 

A.  It  acts  as  a  screen,  to  prevent  the 
wind  from  blowing*  into  the  chimney. 

Q.  What  HARM  would  the  WIND  do  if  it  were 
to  BLOW  into  a  CHIMNEY? 

A.  1st — It  would  prevent  the  smoke 
from  g'etting*  out ;  and 

2dly — The  cold  air  (introduced  into 
the  chimney  by  the  wind)  would  fall 
down  the  flue,  and  drive  the  smoke  with 
it  into  the  room. 

Q.  Why  are  some  things  SOLID,  others  LIQUID, 
and  others  GASEOUS  ? 

A.  Because  the  particles  which  com- 
pose some  thing's  are  nearer  together 
than  they  are  in  others.  Those  in  which 
the  particles  are  closest  are  solid ;  those 


EXPANSION.  109 

in  which  they  are  furthest  apart  are  gas- 
eous  ;  and  *the  rest  liquid. 

Q.  Why  does  heat  change  a  SOLID  (like  ice) 
first  into  a  LIQUID,  and  then  into  a  GAS  ? 

A.  Because  heat  drives  the  compo- 
nent particles  further  asunder  ;  hence  a 
certain  quantity  of  heat  changes  solid  ice 
into  a  liquid — and  a  further  addition  of 
heat  changes  the  liquid  into  steam. 

Q.       Why  does  WATER  SIMMER  before  it  boi/.s  ? 

A.  Because  the  particles  of  water 
near  the  bottom  of  the  kettle  (being*  form- 
ed into  steam  sooner  than  the  rest)  shoot 
upwards;  but  are  condensed,  again  (as 
they  rise)  by  the  colder  water,  and  pro- 
duce what  is  called  "  simmering." 

Q.       What  is  meant  by  SIMMERING  ? 

A.  A  gentle  tremor  or  undidation  on 
the  surface  of  the  water.  When  water 
simmers,  the  bubbles  collapse  beneath  the 
surface,  and  the  steam  is  condensed  to 
water  again ;  but  when  water  boils,  the 
bubbles  rise  to  the  surface,  and  the  steam 
is  thrown  off. 

Collapse,  i.  e.,  burst. 

Q.  Why  does  a  KETTLE  SING  when  the  water 
simmers  ? 

A.  Because  the  air  (entangled  in  the 
water)  escapes  by  Jits  and  starts  through 


110  EFFECTS    OF    HEAT. 

the  spout  of  the  kettle,  which  makes  a 
noise  like  a  wind  instrument. 

Q.  Wh,y  does  NOT  a  kettle  SING  when  the  water 
BOILS? 

A.  Because  all  the  water  is  boiling 
hot ;  so  the  steam  escapes  in  a  continu- 
ous stream,  and  not  by  Jits  and  starts. 

Q.       When  does  a  kettle  sing  MOST? 

A.     When  it  is  set  on  the  hob  to  boil. 

Q.  Why  does  a  kettle  SING  MORE  when  it  is  set 
on  the  SIDE  of  a  fir e,  than  when  it  is  set  in  the  MIDST 
of  the  fire? 

A.  Because  the  heat  is  applied  so 
unequally,  that  one  side  is  made  hotter 
than  the  other  ;  in  consequence  of  which, 
the  steam  is  more  entangled. 

Q.  Why  does  a  KETTLE  sing,  when  the  boiling 
water  begins  to  COOL  again  ? 

A.  Because  the  upper  surface  cools 
first ;  and  the  steam  (which  rises  from 
the  lower  part  of  the  kettle)  is  again  en- 
tangled, and  escapes  by  Jits  and  starts. 

Q.        Why  does  BOILING  WATER  SWELL  ? 

A.  Because  it  is  expanded  by  the  heat : 
i.  e. — The  heat  of  the  fire  drives  the  par- 
ticles of  water  farther  apart  from  each 
other:  and  (as  they  are  not  packed  so  close- 
ly together)  they  take  up  more  room ;  in 
other  words,  the  water  swells. 


EXPANSION.  Ill 

Q.  What  is  meant  when  it  is  said,  that  "  HEAT 
drives  the  PARTICLES  of  water  further  APART  from 
each  other  ?" 

A.  Water  is  composed  of  little  glo- 
bules, like  very  small  grains  of  sand ;  the 
heat  drives  these  particles  away  from 
each  other ;  and  (as  they  then  require 
more  room)  the  water  swells. 

Q.       Why  does  BOILING  WATER  BUBBLE? 

A.  Because  the  vapor  (rising  through 
the  water)  is  entangled,  and  forces  up 
bubbles  in  its  effort  to  escape. 

N.  B.    All  the  air  of  water  is  expelled  at  the  commence- 
ment of  its  boiling. 

Q.       Why  does  a  KETTLE  sometimes  BOIL  OVER  ? 

A.  Because  the  water  is  expanded  by 
heal ;  if,  therefore,  a  kettle  is  filled  icith 
cold  water,  some  of  it  must  run  over,  as 
soon  as  it  is  expanded  by  heat. 

Q.  But  I  have  seen  a  KETTLE  BOIL  OVER,  al- 
though it  has  not  been  filled  FULL  of  WATER  ;  how  do 
you  account  for  THAT? 

A.  If  a  fire  be  very  fierce,  the  air  and 
vapor  are  expelled  so  rapidly,  that  the 
bubbles  are  very  numerous ;  and  (tower- 
ering  one  above  another)  reach  the  top 
of  the  kettle,  and  fall  over. 

Q.  Why  is  a  pot  (which  was  full  to  OVER- 
FLOWING, while  the  water  was  boiling  HOT)  NOT 
PULL,  after  it  has  been  taken  off  the  fire  for  a  short 
time? 


112  EFFECTS   OF   HEAT. 

A.  Because  (while  the  water  is  boil- 
ing) it  is  expanded  by  the  heat,  and  fills 
the  pot  even  to  overflowing  :  but,  when 
it  becomes  cool,  it  contracts  again,  and 
occupies  a  much  less  space. 

Q.  Why  does  the  water  of  a  KETTLE  run  out 
of  the  SPOUT  when  it  BOILS  ? 

A.  Because  the  lid  fits  so  tightly,  that 
the  steam  cannot  lift  it  up  and  escape  : 
being  confined,  therefore,  in  the  kettle,  it 
presses  on  the  water  with  great  power, 
and  forces  it  out  of  the  spout. 

Q.  What  causes  the  RATTLING  NOI&E,  so  often 
made  by  the  LID  of  a  saucepan  or  boiler  ? 

A.  The  steam  (seeking  to  escape) 
forces  up  the  lid  of  the  boiler,  and  the 
weight  of  the  lid  carries  it  back  again  : 
this  being  done  frequently,  produces  a 
rattling  noise. 

Q.  If  the  steam  COULD  NOT  LIFT  UP  THE  LID 
of  the  boiler  how  would  it  escape  ? 

A.  If  the  lid  fitted  so  tightly,  that  the 
steam  could  not  raise  it  up,  the  boiler 
would  burst  into  fragments ,  and  the  con- 
sequences might  be  fatal. 

Q.  When  steam  pours  out  from  the  spout  of  a 
kettle,  the  STREAM  begins  apparently  HALF  AN  INCH 
off  the  SPOUT  ;  why  does  it  not  begin  CLOSE  to  the 

ut? 

A.     Steam  is  really  invisible  ;  and  the 


EXPANSION.  113 

half-inch  (between  the  spout  and  the 
"  stream  of  mist",  is  the  real  steam,  before 
it  has  been  condensed  by  air. 

Q.  Why  is  not  ALL  the  steam  INVISIBLE  as 
well  as  that  half-inch  ? 

A.  Because  the  invisible  particles  are 
condensed  by  the  cold  air ;  and,  rolling 
one  into  another,  look  like  a  thick  mist. 

Q.  What  BECOMES  of  the  STEAM  ?  for  it  soon 
vanishes. 

A.  After  it  has  been  condensed  into 
mist,  it  is  dissolved  by  the  air,  and  dispers- 
ed abroad  as  invisible  vapor. 

Q.      And  what  BECOMES  of  the  INVISIBLE  VAPOR  ? 

A.  Being*  lighter  than  air,  it  ascends  to 
the  upper  regions  of  the  atmosphere, 
where  (being  again  condensed)  it  contri- 
butes to  form  clouds. 

Q.  Why  does  a  METAL  SPOON  (left  in  a  sauce- 
pan) RETARD  the  process  of  BOILING  ? 

A.  Because  the  metal  spoon  (being 
an  excellent  conductor)  carries  off  the  heat 
from  the  water ;  and  (as  heat  is  carried 
off  by  the  spoon)  the  water  takes  a  long- 
er time  to  boil. 

Q.  Why  will  a  POT  (filled  with  water)  NEVER 
BOIL,  when  immersed  in  ANOTHER  vessel  full  of  water 
also  ? 

A.  Because  water  can  never  be  heat- 
ed above  the  boiling  point ;  all  the  heat 


114  EFFECTS    OF    HEAT. 

absorbed  by  water  after  it  boils,  is  em- 
ployed in  generating  steam. 

Q.  How  does  the  conversion  of  water  into  steam, 
prevent  the  INNER  POT  from  BOILING? 

A.  Directly  the  water  in  the  larger 
pot  is  boiling  Jwt  (or  212°),  steam  is  form- 
ed  and  carries  off  some  of  its  lieat ;  there- 
fore, 212°  of  heat  can  never  pass  through 
it,  to  raise  the  inner  vessel  to  boiling 
heat. 

Q.  Why  do  SUGAR,  SALT,  tyc.,  RETARD  the  pro- 
cess of  BOILING  ? 

A.  Because  they  increase  the  density 
of  water ;  and  whatever  increases  the 
density  of  a  fluid,  retards  its  boiling. 

Q.  If  you  want  water  to  boil  without  COMING- 
IN  CONTACT  with  the  SAUCEPAN,  what  plan  must  you 
adopt  ? 

A.  We  must  immerse  the  pot  (contain- 
ing the  water  to  be  boiled)  in  a  sauce- 
pan containing  strong  brim,  or  sugar. 

Q  Why  ivould  the  INNER  vessel  boil,  if  the 
OUTER  vessel  contained  strong  BRINE  ? 

A.  Because  brine  will  not  boil,  till  it 
is  raised  to  218  or  220°.  Therefore, 
212°  of  heat  may  easily  pass  through 
it,  to  raise  the  vessel  immersed  in  it  to  boil- 
ing heat. 

Q.  Why  will  brine  impart  to  another  vessel 
MORE  than  212°,  and  water  NOT  so  MUCH  ? 


EXPANSION.  115 

A.  Because  no  liquid  can  impart  so 
high  a  degree  of  heat,  as  its  own  boiling 
temperature  :  As  water  boils  at  212°  it 
cannot  impart  212°  of  heat :  but,  as  brine 
will  not  boil  without  21°  of  heat,  it  can 
impart  enough  to  make  water  boil. 

Q.  Why  can  liquids  impart  no  EXTRA  heat, 
after  they  boil  ? 

A.  Because  all  extra  heat  is  spent  in 
making  steam.  Hence  water  will  not 
boil  a  vessel  of  water  immersed  in  it,  be- 
cause it  cannot  impart  to  it  212°  of 
heat ;  but  brine  will,  because  it  can  im- 
part more  than  212°  of  heat,  before  it  is 
itself  converted  into  steam. 


Ether  boils  at  -  -  100   c 

Alcohol 173* 

Water 212 

Water,  with  one- 
fifth  salt  -  -  219 


Syrup  boils  at  -  -  221  t 
Oil  of  turpentine  -  314 
Sulphuric  acid  -  -  472 

Linseed  oil 640 

Mercury 656 


Any  liquid  which  boils  at  a  lower  degree  can  be  made  to 
boil,  if  immersed  in  a  liquid  which  boils  at  a  higher  degree. 
Thus  a  cup  of  ether  can  be  made  to  boil  in  a  saucepan  of 
water.  A  cup  of  water  in  a  saucepan  of  brine  or  syrup. 
But  a  cup  of  water  will  not  boil,  if  immersed  in  ether ;  nor 
a  cup  of  syrup  in  water. 

Q.       Why  are  CLOUDS  HIGHER  on  a  FINE  DAY  ? 

A.     Because    they    are    lighter,  and 
more  buoyant. 

Q.       Why  are  CLOUDS  LIGHTER  on  a  FINE  DAY  ? 
A.     1st — Because   the  vapor  of  the 
clouds  is  less  condensed ;  and 


116  EFFECTS    OF    HEAT. 

2dly — The  air  itself  (on  a  fine  day) 
retains  much  of  its  vapor  in  an  invisible 
form. 

Q.  Why  is  a  CUP  put  INVERTED  into  a  FRUIT- 
PIE? 

A.  Its  principal  use  is  to  hold  the, 
crust  up,  and  prevent  it  from  sinking, 
when  the  cooked  fruit  gives  way  under  it. 

Q.  Does  not  the  cup  PREVENT  the  FRUIT  of  the 
pie  from  BOILING  OVER  ? 

A.  No — it  will  rather  tend  to  make  it 
boil  over,  as  there  will  be  less  room  in 
the  dish. 

Q.      Explain  this. 

A.  When  the  pie  is  put  into  the  oven 
the  air  in  the  cup  will  begin  to  expand, 
and  drive  every  particle  of  juice  from 
under  it ;  in  consequence  of  which,  the 
pie-dish  will  have  a  cup-full  less  room  to 
hold  its  fruit  in,  than  if  the  cup  were 
taken  out. 

Q.  If  the  juice  is  driven  OUT  of  the  cup,  why  is 
the  CUP  always  FULL  of  JUICE  when  the  pie  is  cue  up  ? 

A.  Because  immediately  the  pie  is 
drawn,  the  air  in  the  cup  begins  to  con- 
dense again,  and  occupy  a  smaller  space  ; 
and,  as^  the  cup  is  no  longer  full  of  air, 
juice  rushes  in  to  occupy  the  void. 

Q.       Why  does  JUICE  rush  into  the  cup  when  the. 

CUp  is  NOT  FULL  of  AIR  ? 


EXPANSION    FROM    HEAT.  117 

A.  Because  the  external  air  presses 
upon  the  surface  of  the  juice,  which  rushes 
unobstructed  into  the  cup;  as  mercury 
rises  through  the  tube  of  a  barometer. 

N.  B.  Since  the  juice  of  the  pie  runs  into  the  cup,  as 
soon  as  it  is  taken  out  of  the  oven ;  the  cup  prevents  the 
juice  from  being  spilt  over  the  crust,  when  the  pie  is  carried 
about  from  place  to  place ;  although  it  does  not  prevent 
the  fruit  from  boiling  over. 


CHAPTER    XII. 
EXPANSION  FROM  HEAT. 

(Continued.) 

Q.  Does  heat  expand  everything  ELSE  besides 
air  and  water  ? 

A.  Yes  :  every  thing1  (that  man  is  ac- 
quainted with)  is  expanded  by  heat. 

Q,  Wliy  does  a  COOPER  heat  his  HOOPS  RED 
HOT  when  he  puts  them  on  a  tub  ? 

A.  1st — As  iron  expands  by  heat,  the 
hoops  will  be  larger  when  they  are  red 
hot ;  in  consequence  of  which,  they  will 
fit  on  the  tab  more  easily:  and 

2dly — As  iron  contracts  by  cold,  the 
hoops  will  shrink  as  they  cool  down,  and 
girt  the  tub  with  a  tighter  grasp. 

Q.  Why  does  a  WHEELWRIGHT  make  the  hoops 
RED  HOT  which,  he  fixes  on  the  NAVE  of  a  WHEEL? 


118  EFFECTS    OF    HEAT. 

A.  1st — That  they  may  ft  on  more 
easily :  and 

2dly — That  they  may  girt  the  nave 
more  tightly. 

Q.  Why  will  the  wheelwright's  HOOP  FIT  the 
nave  MORE  BASIL Y,for  being  made  RED  HOT? 

A.  Because  it  will  be  expanded  by 
the  heat ;  and  (being  larger)  will  go  on 
the  nave  more  easily. 

Q.  Why  will  the  HOOPS  which  have  been  PUT 
ON  HOT  GIRT  the  nave  more  FIRMLY  ? 

A.  Because  they  will  shrink  when 
they  cool  down ;  and,  therefore,  girt  the 
nave  with  a  tighter  grasp. 

Q.  Why  does  a  STOVE  make  a  CRACKLING 
NOISE  when  afire  is  very  hot  ? 

A.  f  Because  it  expands  from  the  heat ; 
and  the  parts  of  the  stove  rubbing 
against  each  other,  or  driving  against 
the  bricks,  produce  a  crackling  noise. 

Q.  Wh.y  does  a  STOVE  make  a  similar  CRACK- 
LING NOISE  when  a  large  FIRE  is  TAKEN  DOWN  ? 

A.  Because  it  contracts  again,  when 
the  fire  is  removed ;  in  consequence  of 
which,  the  parts  rub  against  each  other 
again,  and  the  bricks  are  again  disturbed. 

Q.  Why  does  the  PLASTER  round  a  STOVE 
CRACK  and  fall  away? 

A.  Because  (when  the  fire  is  light- 
ed) the  iron-work  expands  more  than 


EXPANSION   FROM    HEAT.  119 

the  brick-work  and  plaster,  and  pushes 
them  away ;  but  (when  the  fire  is  put 
out)  the  metal  shrinks  again,  and  leaves 
the  "  setting77  behind. 

The  " setting"  is  a  technical  word  for  the  plaster,  &c., 
in  immediate  contact  with  the  stove. 

Q.       Why  does  the  PLASTER  FALL  AWAY? 

A.  As  a  chink  is  left  (between  the 
"setting'7  and  the  stove),  the  plaster 
will  frequently  fall  away  from  its  own 
weight. 

Q.       What   OTHER  cause  contributes  to  BRING 

the  PLASTER  DOWN? 

A.  As  the  heat  of  the  fire  varies,  the 
size  oftlie  iron  stove  varies  also ;  and  this 
swelling  and  contracting  keep  up  such 
a  constant  disturbance  about  the  plaster, 
that  it  cracks  and  falls  off,  leaving  the 
fire-place  very  unsightly. 

Q.  Why  does  the  MERCURY  of  a  THERMOMETER 
RISE  in  hot  weather  ? 

A.  Because  heat  expands  the  metal, 
which  (being  increased  in  bulk)  occupies 
a  larger  space ;  and,  consequently,  rises 
higher  in  the  tube. 

Q.  Why  is  a  GLASS  BROKEN  when  HOT  WATER 
is  poured  into  it  ? 

A.  Because  the  inside  of  the  glass  is 
expanded  by  the  hot  water,  and  not  the 


120  EFFECTS    OF    HEAT. 

outside;  so   the  glass   snaps,  in  conse- 
quence of  this  unequal  expansion. 

Q.  Why  is  not  the  OUTSIDE  of  the  GLASS  ex- 
panded by  the  hot  water  as  well  as  the  INSIDE  ? 

A.  Because  glass  is  a  bad  conductor 
of  heat,  and  breaks  before  the  heat  of  the 
inner  surface  is  conducted  to  the  outside. 

Q.  Why  does  a  GLASS  snap  because  the  INNER 
surface  is  HOTTER  than  the  OUTER  ? 

A.  Because  the  inner  surface  is  ex- 
panded and  not  the  outer :  in  conse- 
quence of  which,  an  opposing  force  is 
created,  which  breaks  the  glass. 

Q.  Why  is  a  CHINA  CUP  broken  if  HOT  WATER 
be  poured  over  it,  or  into  it  ? 

A.  Because  it  is  a  bad  conductor; 
and,  as  the  inner  surface  expands  from 
the  heat,  (and  not  the  outer,")  an  opposing 
force  is  created,  which  breaks  the  cup. 

Q.  If  a  GLASS  BEAKER  be  set  on  a  warm  HOB, 
why  does  the  BOTTOM  COME  OFF  ? 

A.  Because  glass  is  a  bad  conductor; 
and  (as  the  bottom  of  the  glass  expands 
from  the  warmth  of  the  hot  stove,  before 
the  sides  are  heated)  the  two  parts  sep- 
arate from  each  other. 


LIQUEFACTION.  121 

' 

CHAPTER  XIII. 

2. LlQJJEFACTION. 

3. — VAPORIZATION. 

Q.       What  is  meant  by  LIQUEFACTION  ? 

A.  The  staf'6  of  being  melted;  as  ice 
is  melted  by  the  heat  of  the  sun., 

Q.       Why  is  ICE  MELTED  by  the  HEAT  of  the  SUN  ? 

A.  Because,  when  the  heat  of  the 
sun  enters  the  solid  ice,  it  forces  its  par- 
ticles asunder ;  till  their  attraction  of 
cohesion  is  sufficiently  overcome,  to 
convert  the  solid  ice  into  a  liquid. 

See  p.  109. 

Q.  Why  are  METALS  MELTED  by  the  heat  of 
FIRE  ? 

A.  Because,  when  the  heat  of  the 
fire  enters  the  solid  metal,  it  forces  Us  par- 
tides  asunder;  till  their  attraction  of 
cohesion  is  sufficiently  overcome,  to  con- 
vert the  solid  metal  into  a  liquid. 

Q.  Why  is  WATER  converted  into  STEAM  by 
the  heat  of  the  FIRE  ? 

A.  Because,  when  the  heat  of  the 
fire  enters  the  water,  it  separates  its 
globules  into  very  minute  bubbles  ;  which 
(being1  lighter  than  air)  fly  off  from  the 
surface  in  the  form  of  steam. 

Q.       Why  does  not  WOOD  MELT  like  metal  ? 
6 


122  EFFECTS    OF    HEAT. 

A.  Because  the  heat  of  the  fire  de- 
composes the  wood  into  gas,  smoke,  and 
ashes;  and  the  different  parts  separate 
from  each  other. 

Q.       What  is  meant  by  VAPORIZATION  ? 

A.  The  conversion  of  a  solid  or  liquid 
into  vapor:  as  snow  or  water  is  con- 
verted into  vapor  by  the  heat  of  the 
sun. 

Q.       What  are  CLOUDS  ? 

A.  Moisture  evaporated  from  the 
earth,  and  again  partially  condensed  in 
the  upper  regions  of  the  air. 

Q.  What  is  the  difference  between  a  FOG  and  a 
CLOUD  ? 

A.  Clouds  and  fogs  differ  only  in 
one  respect.  Clouds  are  elevated  above 
our heads :  but  fogs  come  in  contact  with 
the  surface  of  the  earth. 

Q.       Why  do  CLOUDS  FLOAT  so  readily  in  the  air  ? 

A.  Because  they  are  composed  of 
very  minute  globules  (called  ves'icles) ; 
which  (being  lighter  than  air)  float,  like 
soap  bubbles. 

Q.  Why  does  VAPOR  sometimes  form  into 
CLOUDS,  and  sometimes  rest  upon  the  earth  as  MIST 
or  FOG? 

A.  This  depends  on  the  temperature 
of  the  air.  When  the  surface  of  the 
earth  is  warmer  than  the  air,  the  vapor 


VAPORIZATION.  123 

of  the  earth  (being*  condensed  by  the 
chill  air)  becomes  mist  or  fog.  Bat, 
when  the  air  is  warmer  than  the  earth, 
the  vapor  rises  through  the  air,  and  be- 
comes cloud. 

Q.      Are  ALL  clouds  ALIKE  ? 

A.  No.  They  vary  greatly  in  density, 
height,  and  color. 

Q.       What  is  the  chief  CAUSE  of  fog  and  CLOUDS  ? 

A.     The  changes  of  the  wind. 

Many  local  circumstances  also  favor  the  formation  of 
clouds. 

Q.  How  can  the  CHANGES  of  the  WIND  affect  the 
CLOUDS  ? 

A.  If  a  cold  current  of  wind  blows 
suddenly  over  any  region,  it  condenses 
the  invisible  vapor  of  the  air  into  cloud 
or  rain :  but  if  a  warm  current  of  wind 
blows  over  any  region,  it  disperses  the 
clouds,  by  absorbing  their  vapor. 

Q.       What  COUNTRIES  are  the  MOST  cloudy  ? 

A.  Those  where  the  winds  are  most 
variable,  as  Britain. 

Q.       What  COUNTRIES  are  the  LEAST  cloudy  ? 

A.  Those  where  the  winds  are  least 
variable,  as  Egypt. 

Q.       What  DISTANCE  are  the  CLOUDS  from  the 

EARTH  ? 

A.  Some  thin,  light  clouds  are  eleva- 
ted above  the  highest  mountain-top ; 


124  EFFECTS    OF    HEAT. 

some  heavy  ones  touch  the  steeples, 
trees,  and  even  the  earth  :  but  the  aver- 
age height  is  between  one  and  two  miles. 

N.  B.     Streaky,  curling  clouds,  like  hair,  are  often  5  or 
6  miles  high. 

Q.      WHAT  CLOUDS  are  the  LOWEST  ? 

A.  Those  which  are  most  highly  elec- 
trified; lightning*  clouds  are  rarely  more 
than  about  700  yards  above  the  ground  ; 
arid  often  actually  touch  the  earth  with 
one  of  their  edges. 

Q.       What  is  the  SIZE  of  the  CLOUDS? 

A.  Some  clouds  are  20  square  miles 
in  surface,  and  above  a  mile  in  thickness  ; 
while  others  are  only  a  few  yards  or 
inches. 

Q.  How  can  persons  ascertain  the  THICKNESS 
of  a  cloud  ? 

A.  As  the  tops  of  high  mountains  are 
generally  above  the  clouds,  travellers 
may  pass  quite  through  them  into  a  clear 
blue  firmament  ;  when  the  clouds  will 
be  seen  beneath  their  feet. 

Q.  What  produces  the  great  VARIETY  in  the 
SHAPE  of  the  CLOUDS? 

A.  Three  things  :  1st — The  cause 
and  manner  of  their  formation  : 

2dly — Their  electrical  condition  :    and 
3dly — Their   relations  to  currents  of 
wind. 


VAPORIZATION.  125 

Q.  How  can  ELECTRICITY  affect  the  SHAPE  of 
CLOUDS? 

A.  If  one  cloud  be  'full  of  electricity 
and  another  not,  they  will  be  attracted  to 
each  other,  and  either  coalesce — dimi- 
nish in  size — or  vanish  altogether. 

Q.  WHAT  CLOUDS  assume  the  most  FANTASTIC 
shapes  ? 

A.  Those  that  are  the  most  highly 
electrified. 

Q.  What  effect  have  WINDS  on  the  SHAPE  of 
CLOUD  ? 

A.  They  sometimes  absorb  them  en- 
tirely;  sometimes  increase  their  volume 
and  density ;  and  sometimes  change  the 
position  of  their  parts. 

Q.       How  can  WINDS  ABSORB  CLOUDS  altogether? 

A.  Warm,  dry  winds  will  convert  the 
substance  of  clouds  into  invisible  vapor, 
which  they  will  carry  away  in  their  own 
current. 

Q.  How  can  WINDS  INCREASE  the  bulk  and 
density  of  CLOUDS  ? 

A.  Cold  currents  of  wind  will  con- 
dense the  invisible  vapor  of  the  air,  and 
add  it  to  the  clouds  with  which  they 
come  in  contact. 

Q.  How  can  winds  CHANGE  the  SHAPE  of 
CLOUDS,  by  altering  the  position  of  their  parts  ? 

A.     Clouds  are  so  voluble   and  light, 


126  EFFECTS    OF    HEAT. 

that  every  breath  of  wind  changes  the  po- 
sition of  their  ves'icles  or  bubbles. 

Q.  What  are  the  general  COLORS  of  the 
CLOUDS  ? 

A.  White  and  grey,  when  the  sun  is 
above  the  Jiorizon :  but  red,  orange,  and 
yellow,  at  sun-rise  and  sun-set. 

The  blue  sky  is  not  cloud  at  all. 
Q.       Why  are  thz  LAST  CLOUDS  of  EVENING  gen- 
erally of  a  RED  tinge? 

A.  Because  red  rays  (being  the  least 
refrangible  of  all)  are  the  last  to  disap- 
pear. 


Suppose  P  A  to  be  the  red  rays,  P  B  the  yellow,  P  C 
the  blue.  If  the  earth  turns  in  the  direction  of  P  A  D,  it 
is  quite  manifest  that  a  spectator  will  see  A,  (the  red  rays,) 
some  time  after  P  C  and  P  B  have  passed  from  sight. 

Q.  What  is  meant  by  being  "  LESS  REFRANGI- 
BLE "? 

A.  Being  less  able  to  be  bent.  Blue 
and  yellow  rays  are  more  easily  bent 
below  the  horizon  by  the  resistance  of  the 
air :  but  red  rays  are  not  so  much  bent, 


VAPORIZATION.  127 

down ;  and,  therefore,  we  see  them  later 
in  the  evening. 

As  at  A  in  the  figure  on  p.  126. 
Q.       Why  are  MORNING  CLOUDS  generally  of  a 
RED  tinge? 

A.  Because  red  rays  are  the  least  re- 
frangible  of  all;  and  not  being  bent  so 
much  as  blue  and  yellow  rays,  we  see 
them  sooner  of  a  morning. 

Thus  (fig.  on  p.  126)  if  the  earth  turned  in  the  direction 
of  D  A  P,  a  spectator  at  D  would  see  A  (the  red  rays)  long 
before  he  saw  P  B  and  P  C. 

Q.       Why  is  not  the  color  of  clouds  always  ALIKE  1 

A.  Because  their  size,  density,  and  si- 
tuation in  regard  to  the  sun,  are  perpetu- 
ally varying  ;  so  that  sometimes  one  co- 
lor is  reflected  and  sometimes  another. 

Q.       What  regulates  the  MOTION  of  the  CLOUDS  ? 

A.  Principally  the  winds ;  but  some- 
times electricity  will  influence  their  mo- 
tion also. 

Q.  How  do  you  know  that  CLOUDS  move  by 
OTHER  influences  besides  WIND  ? 

A.  Because  (in  calm  weather)  we 
often  see  small  clouds  meeting  each  other 
from  opposite  directions. 

Q.  How  do  you  know  that  ELECTRICITY  affects 
the  motion  of  the  clouds  ? 

A.  Because  clouds  often  meet  from 
opposite  directions ;  and,  having  discharg- 


128  EFFECTS    OF    HEAT. 

ed  their  opposite  electricities  into  each 
other,  vanish  altogether. 

Q.  Into  how  many  CLASSES  are  the  different 
sorts  of  CLOUDS  generally  divided  ? 

A.  Into  three  classes  : — viz.  Simple, 
Intermediate,  and  Compound. 

Q.       How  are  SIMPLE  CLOUDS  sub-divided  ? 

A.  Into  1. — Cirrus;  2. — Cum'ulus  ; 
and  3. — Stra'tus  clouds. 

Q.       What  sort  of  CLOUDS  are  called  CIRRUS  ? 

A.  Clouds  like  fibres,  loose  hair,  or 
thin  streaks,  are  called  "  cirrus  clouds." 

Q.       Why  are  these  clouds  called  CIRRUS  ? 

A.  From  the  Latin  word  cirrus  ("  a 
lock  of  hair,  or  curl  ").  Cirrus  clouds 
are  the  most  elevated  of  all. 

Q.       What  do  CIRRUS  clouds  PORTEND? 

A.  When  the  streamers  point  up- 
wards, the  clouds  are  falling,  and  rain  is 
at  hand :  but  when  the  streamers  point 
downwards,  westerly  winds  or  drought 
may  be  expected. 

Q.       What  sort  of  CLOUDS  are  called  CUM'ULUS  ? 

A.  Cum'ulus  clouds  are  lumps,  like 
great  sugar-loaves — volumes  of  smoke — 
or  mountains  towering  over  mountains. 

Q.  Why  are  these  monster  masses  called  CUM'- 
ULUS CLOUDS  ? 

A.  From  the  Latin  word  cumulus 
("  a  mass  or  pile  "). 


VAPORIZATION.  129 

Q  What  do  CUM'ULTJS  clouds  FORESHOW  1 
A.  When  these  piles  of  cloud  are 
fleecy,  and  sail  against  the  wind,  they 
indicate  rain;  but  when  their  outline  is 
very  hard,  and  they  come  up  with  the 
wind,  they  foretell  fine  iveather. 

Cum/ulus  clouds  should  be  smaller  towards  evening 
than  they  are  at  noon.  If  they  increase  in  size  at  sun-set, 
a  thunder-storm  may  be  expected  in  the  night. 

Q.       What  sort  of  CLOUDS  are  calkd  STRA'TUS  ? 

A.  Creeping  mists,  especially  preva- 
lent in  a  summer's  evening :  these  clouds 
rise  at  sun-set  in  low,  damp  places ;  and 
are  always  nearer  the  earth  than  anjr 
other  sort  of  cloud. 

Q.       Why  are,  these,  mists  called  STRA'TUS  clouds  ? 

A.  From  the  Latin  word  stra'tus 
("  laid  low,"  or  "  that  which  lies  low  "). 

Q.       What  produces  CIRRUS  CLOUDS  1 

A.  Moisture  in  a  visible  form,  deposit- 
ed in  the  higher  regions  of  the  atmos- 
phere by  ascending  currents  of  heated  air, 

Q.       What  produces  CUM'ULUS  CLOUDS  ? 

A.  Masses  of  visible  vapor  passing 
from  the  places  where  they  were/ormed, 
to  other  places  where  they  are  about  to 
be  either  dissolved,  or  deposited  as  falling 
rain. 

Q.       What  produces  STRA'TUS  CLOUDS  ? 

A.  Beds  of  visible  moisture,  formed 
6* 


130  EFFECTS    OF    HEAT. 

by  some  chilling-  effects,  acting-  along-  the 
direct  surface  of  the  earth. 

Q.  How  are  the  INTERMEDIATE  CLOUDS  sub-di- 
vided ? 

A.  Into  two  sorts.  1.— -The  Cirro- 
Cum'ulus ;  and  2. — The  Cirro-Stra'tus. 

Q.       What  are  CIRRO-CUM'ULUS  CLOUDS? 

A.  Cirro-Cum'ulus  clouds  are  cirrus 
clouds  -springing-  from  a  massy  centre  ; 
or  heavy  masses ,  edg-ed  with  long  streaks 
g-enerally  called  "mares'  tails." 

A  system  of  small  round  clouds  may  be  called  cirro- 
<cum'ulus. 

Q.       What  do  CIRRO-CUM'ULUS  clouds  generally 

TOREBODE  ? 

A.  Continued  drought,  or  hot,  dry 
weather. 

Q.       What  are  CIRRO-STRA'TUS  CLOUDS  ? 

A.  They  compose  what  is  generally 
called  a  "  mackarel  sky."  This  class  of 
clouds  *  invariably  indicates  rain  and 
wind  ;  hence  the  proverb — 

"  Mackarel's  scales  and  mares'  tails 
Make  lofty  ships  to  carry  low  sails." 

Q.       Wliat  produce  CIRRO-CUM'ULUS  clouds  ? 

A.  Cumulus  clouds  dissolving  away 
into  cirrus  produce  the  intermediate  class, 
called  CIRRO-CUM'ULUS. 

Q.       What  produce  CIRRO-STRA'TUS  clouds  ? 

A.     Cirrus  clouds  accumulating  into 


VAPORIZATION.  131 

denser  masses  produce  the  intermediate 
class,  called  CIRRO-STRA'TUS. 

Q.       How  are  COMPOUND  CLOUDS  sub-divided? 

A.  Compound  clouds  are  also  sub- 
divided into  two  sorts.  1. — The  Cum'u- 
lo-Stra'tus  ;  and  2. — The  Nimbus  clouds. 

Q.       What  is  meant  by  CUMULO-STRA'TUS  clouds  ? 

A.  Those  clouds  which  assume  all 
sorts  of  gigantic  forms ;  such  as  vast 
towers  and  rocks — huge  whales  and 
dragons — scenes  of  battle — and  cloudy 
giants.  This  class  of  clouds  is  the  most 
romantic  and  strange  of  all. 

Q.       What    do    the    CUMULO-STRA'TUS    clouds 

FORETELL  ? 

A.  A  change  of  weather ;  either  from 
fine  to  rain,  or  from  rain  to  fine. 

Q.       What  are  NIMBUS  CLOUDS  ? 

A.  All  clouds  from  which  rainfalls. 
Nimbus  is  the  Latin  word  for  "  clouds 
which  bring  a  storm" 

Q.  By  what  particular  character  may  the 
NIMBUS  (or  rain-cloud)  be  at  once  DISTINGUISHED  ? 

A.  By  the  want  of  a  defined  outline  : 
Its  edge  is  gradually  shaded  off  from  the 
deep  grey  mass  into  transparency. 

Q.  What  APPEARANCE  takes  place  in  the  CLOUDS 
at  the.  approach  of  RAIN  ? 

A     The  cum'ulus  cloud  becomes  sta- 


132  EFFECTS    OF    HEAT. 

tionary,  and  cirrus  streaks  settle  upon  it, 
forming  cum'ulo-stratus  clouds ;  black  at 
first,  but  afterwards  of  a  grey  color. 

Q.  Why  do  CLOUDS  gather  ROUND  MOUNTAIN 
TOPS  ? 

A.  Because  the  air  (being-  chilled  by 
the  cold  mountain  tops)  deposits  its  va- 
por there  in  a  visible  form  or  cloud. 

Q.       What  are  the  USES  of  CLOUDS  ? 

A.  1st — They  act  as  screens,  to  ar- 
rest the  radiation  of  heat  from  the  earth  ; 

2dly — They  temper  the  heat  of  the 
sun's  rays ;  and 

3dly — They  are  the  great  store-houses 
of  rain. 

11  Radiation  of  heat,"  i.  e.,  the  escape  of  heat,  when  no 
conductor  carries  it  away. 

Q.       Why  is  WIND  said  to  BLOW  UP  the  CLOUDS  ? 

A.  Because  a  dry,  warm  wind  (which 
has  travelled  over  seas)  having  absorbed 
a  large  quantity  of  moisture,  deposits 
some  of  it  in  the  visible  form  of  clouds, 
as  soon  as  it  reaches  a  colder  region  of 
air. 

Q.  Why  does  WIND  sometimes  DRIVE  AWAY  the 
CLOUDS  ? 

A.  Because  it  has  travelled  over  dry 
climes  or  thirsty  deserts,  and  become  so 
dry,  that  it  absorbs  vapor  from  the 
clouds,  and  causes  them  to  disappear. 


VAPORIZATION.  133 

Q.       What  is  the  CAUSE  of  a  RED  SUN-SET? 

A.  The  vapor  of  the  air,  not  being* 
actually  condensed  into  clouds,  but  only 
on  the  point  of  being  condensed. 

Q.  Why  is  a  RED  SUN-SET  an  indication  of  a 
FINE  DAY  to-morrow  ? 

A.  Because  the  vapors  of  the  earth 
are  not  condensed  into  clouds,  by  the  cold 
of  sunset.  Our  Lord  referred  to  this 
prognostic  in  the  following"  words : 
"  When  it  is  evening-  ye  say  it  will  be 
fair  weather,  for  the  sky  is  red."  (Matt, 
xvi.  2.) 

Q.       What  is  the  cause  of  a  coppery  YELLOW 

SUN -SET  ? 

A.  The  vapor  of  the  air  being*  actu- 
ally condensed  into  clouds. 

Q.  Why  do  vapors  (NOT  ACTUALLY  CONDENSED) 
refract  RED  rays,  while  condensed  vapor  refracts 
yellow  ? 

A.  Because  the  beams  of  light  meet 
with  very  little  resistance ;  in  conse- 
quence of  which,  those  rays  are  bent 
down  to  the  eye,  which  require  the  least 
refraction,  such  as  red. 

See  figure  on  p.  126,  where  it  is  evident  that  the  red  ray 
P  A,  is  less  bent,  than  the  yellow  and  blue  rays,  P  B,  P  C. 

Q.  Why  do  CONDENSED  vapors  refract  YEL- 
LOW rays,  whereas  vapors  not  actually  condensed 
refract  red  ? 

A.     Because  the  beams  of  light  meet 


134  EFFECTS    OF    HEAT. 

with  more  resistance  from  the  condensed 
vapor ;  in  consequence  of  which,  those 
rays  are  bent  down  to  the  eye,  which  are 
more  refracted  than  the  red,  such  as  yel- 
low. 

See  on  figure  p.  126,  where  it  is  evident  that  the  yellow 
ray,  P  B,  is  more  bent  than  the  red  ray,  P  A. 

Q.  Why  is  a  YELLOW  SUN-SET  an  indication 
of WET  ? 

A.  Because  it  shows  that  the  vapors 
of  the  air  are  already  condensed  into 
clouds ;  rain,  therefore,  may  be  shortly 
expected. 

Q.       What  is  the  cause  of  a  RED  SUN-RISE  ? 

A.  Vapor  in  the  upper  region  of  the 
air  just  on  the  point  of  being  condensed. 

Q.  Why  is  a  RED  and  LOWERING  sky  at  SUN- 
RISE an  indication  of  a  WET  DAY  ? 

A.  Because  the  higher  regions  of  the 
air  are  laden  with  vapor  on  the  very 
point  of  condensation,  which  the  rising 
sun  cannot  disperse.  Hence  our  Lord's 
observation,  "  In  the  morning  ye  say,  it 
will  be  foul  weather  to-day,  for  the  sky 
is  red  and  lowering."  (Matt.  xvi.  3.) 

Q.       Why  is  a  GREY  MORNING  an  indication  of 

a  FINE  DAY  ? 

A.  Because  only  the  air  contiguous  to 
the  earth  is  damp  and  full  of  vapor. 
There  are  no  vapors  in  the  higher  re- 


VAPORIZATION.  135 

gions  of  the  air,  to  bend  down  to  the  eye 
even  the  red  rays  of  any  beam  of  light. 

Q.  What  difference  (in  the  state  of  the  air)  is 
required,  to  make  a  GREY  and  RED  SUN-RISE  1 

A.  In  a  grey  sun-rise,  only  that  por- 
tion of  air  contiguous  to  the  earth  is  filled 
with  vapor ;  all  the  rest  is  clear  and  dry. 
But  in  a  red  sun-rise  the  air  in  the  upper 
regions  is  so  full  of  vapor,  that  the  rising 
sun  cannot  disperse  it. 

Q.  Why  is  a  GREY  SUN-SET  an  indication 
of  WET  ? 

A.  Because  it  shows  that  the  air  on 
the  surface  of  the  earth  is  very  damp  at 
sun-set ;  which  is  a  plain  proof  that  the 
air  is  saturated  with  vapor ;  in  conse- 
quence of  which  wet  may  be  soon  ex- 
pected :  hence  the  proverb — 

"  Evening  red  and  morning  grey 
Will  set  the  traveller  on  his  way ; 
But  evening  grey  and  morning  red 
Will  bring  down  rain  upon  his  head." 

Q.  What  is  meant  by  an  AURORA  BOREA'LIS, 
or  northern  light  ? 

A.  Luminous  clouds  in  the  north  of 
the  sky  at  night-time.  Sometimes  streaks 
of  blue,  purple,  green,  red,  &c.,  and 
sometimes  flashes  of  light,  are  seen. 

Q.  What  is  the  cause  of  the  AURORA  BOREA'- 
LIS/  or  northern  light  1 


136  EFFECTS    OF    HEAT. 

A.  Electricity  in  the  higher  regions 
of  the  atmosphere. 

Q.  Why  are  there  DIFFERENT  COLORS  in  the 
Aurora  Borea'iis,  such  as  white,  yellow,  red  and 
purple  ? 

A.  Because  the  electric  fluid  passes 
through  air  of  different  densities.  The 
most  rarefied  air  produces  a  white  ligfti  ; 
the  most  dry  air,  red;  and  the  most 
damp  produces  yellow  streaks. 

Q.  Does  the  AURORA  BOREA'LIS  forebode  fine 
weather  or  WET  ? 

A.  When  its  coruscations  are  very 
bright,  it  is  generally  followed  by  unset- 
tled weather. 

Q.  Why  does  a  HAZE  round  the  SUN  indicate 
RAIN  ? 

A.  Because  the  haze  is  .caused  by 
very  fine  rain  falling  in  the  upper  regions 
of  the  air :  when  this  is  the  case,  a  rain 
of  5  or  6  hours'1  duration  may  be  expected. 

Q.  Why  is  a  HALO  round  the  MOON  a  sure  in- 
dication of  RAIN  ? 

A.  Because  it  is  caused  by  fine  rain, 
falling  in  the  upper  regions  of  the  air. 
The  larger  the  halo,  the  nearer  the  rain- 
clouds,  and  the  sooner  may  rain  be  ex- 
pected. 

Q.  What  is  the  cause  of  a  BLACK  MIST  :  and 
why  does  it  bring  WET  weather  ? 


WEATHER.  137 

A.  Tbe  mist  is  black,  because  it  is 
overshadowed  by  dense  clouds;  and  wet 
weather  may  be  expected,  because  the 
air  is  saturated  with  vapor. 

Q.  Why  is  MIST  sometimes  WHITE  :  and  why 
does  a  white  mist  indicate  FINE  weather  ? 

A.  The  mist  is  white,  because  no 
clouds  blacken  it  with  their  shadow ;  and 
fine  weather  may  be  expected,  because 
the  sky  is  cloudless. 

Q.  Why  do  we  FEEL  almost  SUFFOCATED  in  a 
hot  cloudy  night  ? 

A.  Because  the  heat  of  the  earth 
cannot  escape  into  the  upper  region  of 
the  air ;  but  is  pent  in  by  the  clouds, 
and  confined  to  the  surface  of  the  earth. 

Q.  Why  do  we  feel  SPRIGHTLY  in  a  clear  ^ 
bright  night  ? 

A.  Because  the  heat  of  the  earth  can 
readily  escape  into  the  upper  regions  of 
the  air,  and  is  not  confined  and  pent  in 
by  thick  clouds. 

Q.  Why  do  we  FEEL  DEPRESSED  in  SPIRITS  on 
a  WET,  murky  DAY  ? 

A.  1st — Because  the  air  is  laden 
with  vapor,  and  has  (proportionally)  less 
oxygen. 

2dly — The  air  being-  lighter  than  usual, 
does  not  balance  the  air  in  our  body ;  and 


138  EFFECTS    OF    HEAT. 

3dly — Moist  air  has  a  tendency  to  de- 
press the  nervous  system. 

Q.  Wliat  is  meant  by  the  "  air  balancing  the 
air  in  our  body  ?" 

A.  The  human  body  contains  air  of 
a  given  density ;  if,  therefore,  we  ascend 
into  rarer  air,  or  descend  into  denser,  the 
balance  is  destroyed,  and  we  feel  op- 
pressed. 

Q.  Why  do  we  feel  OPPRESSED,  if  the  air 
around  is  not  of  the  SAME  DENSITY  as  that  in  our 
bodyl 

A.  Because  if  the  air  be  more  dense 
than  our  body,  it  will  produce  a  feeling- 
of  oppression ;  if  it  be  less  dense,  the  air 
in  our  body  will  produce  a  feeling*  of 
distension. 

Q.  Why  do  PERSONS,  who  ASCEND  in  BAL- 
LOONS, FEEL  PAIN  in  their  eyes,  ears,  and  chest  ? 

A.  Because  the  air  in  the  upper  re- 
gions of  the  atmosphere  is  more  rare 
than  the  air  in  their  bodies ;  and  (till 
equilibrium  is  restored)  pain  will  be  felt  in 
the  more  sensitive  parts  of  the  body. 

More  especially  in  the  tympanum  of  the  ear. 
Q.       Why  do  PERSONS,  who  DESCEND  in  DIVING- 
BELLS.  FEEL  PAIN  in  their  eyes,  ears,  and  chest  ? 

A.  Because  the  air  in  the  diving--bell 
is  compressed  by  the  upward  pressure  of 
the  water;  in  consequence  of  which, 


WEATHER.  139 

great  pain  is  felt  in  the  more  sensitive 
parts  of  the  body. 

The  pressure  thus  caused  is  sometimes  sufficient  to  rup- 
ture the  membrane  of  the  tympanum,  and  produce  incu- 
rable deafness. 

Q.  Why  are  PEARL  DIVERS  very  frequently 
DEAF  ? 

A.  Because  the  pressure  of  the  water 
against  the  tympanum  of  their  ears  rup- 
tures the  membrane  ;  and  this  rupture 
produces  incurable  deafness. 

Q.       Why  does  the  SEA  HEAVE  and  SIGH,  just 

PREVIOUS  to  a  STORM  ? 

A.  Because  the  density  of  the  air 
is  very  suddenly  diminished ;  and  (as  the 
density  of  the  air  is  diminished)  its  pow- 
er to  transmit  sound  is  diminished  also  ; 
in  consequence  of  which,  the  roar  of  the 
sea  is  less  audible,  and  seems  like  heavy 
sighs. 

Q.       Why  is  the  AIR  so  universally  QUIET,  just 

PREVIOUS  to  a  TEMPEST  ? 

A.  Because  the  air  is  suddenly  and 
very  greatly  rarejied ;  and  (as  the  density 
of  the  air  is  diminished)  its  power  to 
transmit  sound  is  diminished  also. 

Q.  How  do  you  KNOW,  that  RAREFIED  air 
CANNOT  TRANSMIT  SOUND  so  well  as  dense  air  ? 

A.  Because  the  sound  of  a  bell,  (in 
the  receiver  of  an  air-pump)  can  scarcely 


140  EFFECTS    OF    HEAT. 

be  heard,  after  the  air  has  been  partially 
exhausted  ;  and  the  report  of  a  pistol 
(fired  on  a  high  mountain)  would  be 
scarcely  audible. 

Q.  Why  do  we  FEEL  BRACED  and  LIGHT- 
HEARTED  on  a  FINE  spring  or  FROSTY  morning  ? 

A.  1st — Because  there  is  more  oxy- 
gen in  the  air  on  a  Nfine  frosty  morning*, 
than  there  is  on  a  wet  day :  and 

2dly — A  brisk  and  frosty  air  has  a 
tendency  to  brace  the  nervous  system. 

Q.  Why  do  DOGS  and  CATS  (confined  to  a 
room)  feel  LAZY  and  DROWSY,  at  the  approach  of 
rain  ? 

A.  1st — Because  the  air  does  not 
contain  its  full  proportion  of  oxygen  ;  and 

2dly — The  damp  depresses  their  ner- 
vous system,  and  makes  them  drowsy. 

Q.  When  SHEEP  lie  under  a  HEDGE,  and  seem 
unwilling  to  go  to  pasture,  RAIN  is  at  hand:  Ex- 
plain the  reason  of  this. 

A.,  1st — As  the  air  does  not  contain 
its  full  proportion  of  oxygen,  they  feel 
uneasy;  and 

2dly — As  the  damp  air  relaxes  their 
nervous  system,  they  feel  listless  and 
drowsy. 

Q.  Why  do  HORSES  neigh,  CATTLE  low,  SHEEP 
bleat,  and  ASSES  bray,  at  the  approach  of  rain  ? 

A.     1st — As  the  air  does  not  contain 


WEATHER.  141 

its  full  proportion  of  oxygen,  they  feel 
a  difficulty  in  breathing ;  and 

2dly — As  damp  relaxes  their  nerves, 
they  feel  languid  and  uneasy. 

Q.  Mention  some  OTHER  ANIMALS,  which  indi- 
cate the  approach  of  rain  in  a  similar  way. 

A.  When  pigs  squeak,  as  if  in  great 
pain — frogs  croak  with  a  loud,  hoarse 
noise — owls  screech — woodpeckers  cry 
— peacocks  scream — guinea-fowls  squall 
— or  ducks  and  geese  are  unusually 
noisy,  rain  is  close  at  hand. 

Q.  Why  do  CANDLES  and  FIRES  burn  with  a 
BLUER  FLAME  in  wet  weather  ? 

A.  Because  the  air  contains  less  oxy- 
gen in  wet  weather,  and  therefore,  the 
heat  of  fire  is  less  intense :  The  flame  is 
blue,  because  the  fuel  is  not  thoroughly 
consumed. 

Q.  Why  do  HTLLS,  <$•£.,  appear  LARGER  in 
WET  weather  ? 

A.  Because  the  air  is  laden  with  vapor, 
which  causes  the  rays  of  light  to  diverge 
more ;  in  consequence  of  which,  they  pro- 
duce on  the  eye  larger  images  of  objects. 

Q.  Why  do  TREES,  <^c.,  in  WET  weather  ap- 
pear FURTHER  OFF  than  they  really  are  ? 

A.  Because  the  fog  or  mist  diminish- 
es the  light  reflected  from  the  object ;  and 


142  'EFFECTS    OF    HEAT. 

as  the  object  becomes  more  dim,  it  seems 
to  be  farther  off.     ^ 

Q.  Why  do  CATS  RUB  their  EARS,  when  it  is 
likely  to  rain  ? 

A.  Either  because  the  air  is  full  of 
vapor,  and  its  humidity  (piercing  between 
the  hair  of  the  cat)  produces  an  itching 
sensation :  or  more  probably,  because  the 
air  is  overcharged  with  electricity. 

Q.  How  can  the  ELECTRICITY  of  air  produce  a 
sensation  of  ITCHING  ? 

A.  If  the  air  is  overcharged  with 
electricity,  the  hair  of  the  cat  is  over- 
charged also  ;  and  this  makes  her  feel 
as  if  she  were  covered  with  cobwebs. 

Q.       Why  does  the  CAT  keep  RUBBING  herself? 

A.  Because  her  hair  will  not  Iw 
smooth,  but  has  a  perpetual  tendency  to 
become  turgid  and  ruffled;  so  the  cat 
keeps  rubbing  her  coat  and  ears,  to 
smooth  the  hair  down,  and  brush  away 
the  feeling  of  cobwebs. 

Q.  Why  do  our  HEADS  and  SKIN  itch  before 
rain  ? 

A.  Probably  because  the  air  is  over- 
charged with  electricity ;  and,  therefore, 
a  sensation  (like  that  of  cobwebs)  irri- 
tates the  skin,  and  produces  an  itching. 

Q.       When  the  plants  called  TREFOIL,  DANDE- 


WEATHER.  143 

LION,  PIMPERNEL,  <Jr.,  FOLD  up  their  leaves,  RAIN  is 
always  close  at  hand  :  Explain  this. 

A.  1st — The  cloudy  weather  dimin- 
ishes the  light  of  the  sun ;  and  without 
the  stimulus  of  sun-light,  these  flowers 
never  open  their  leaves. 

2dly — The  vapor  of  the  damp  air,  in- 
sinuating1 itself  into  the  air-vessels  of 
these  delicate  plants,  causes  them  to 
expand ;  in  consequence  of  which,  the 
leaflets  contract  and  close. 

All  these  plants  close  at  sun-set  also. 
Q.       Why  do  DOORS  SWELL  in  RAINY  weather  ? 

A.  Because  the  air  is  filled  with  va- 
por, which  (penetrating1  into  the  pores  of 
the  wood)  forces  the  parts  farther  apart, 
and  swells  the  door. 

Q.       Why  do  DOORS  SHRINK  in  DRY  weather  ? 

A.  Because  the  moisture  is  absorbed 
from  the  wood  ;  and,  as  the  particles  are 
brought  closer  together,  the  size  of  the 
door  is  lessened — in  other  words,  the 
wood  shrinks. 

Q.  Why  is  the  AIR  filled  with  offensive  SMELLS, 
just  previous  to  a  coming  RAIN  ? 

A.  Because  the  volatile  parts  which 
rise  from  dung-hills,  sewers,  &c.,  are  pre- 
vented (by  the  vapor  of  the  air)  from 
rising  so  readily,  as  when  the  sun  is 
shining  brightly. 


144  EFFECTS    OF   HEAT. 

Q.       Why  do   FLOWERS   smell   SWEETER   and 

STRONGER,  just  preVlOUS  tO  RAIN  ? 

A.  Because  the  volatile  parts  which 
constitute  the  perfume  of  flowers,  are 
prevented  (by  the  vapor  of  the  air)  from 
rising ;  in  consequence  of  which,  they 
are  confined  to  the  lower  regions  of  the 
atmosphere. 

N.  B.  Many  essential  oils  and  other  volatile  substances, 
which  produce  odors  in  plants,  require  the  presence  of 
much  moisture  for  their  perfect  development. 

Q.  Why  do  HORSES  and  other  animals  stretch 
out  their  necks,  and  SNUFF  up  the  AIR,  just  previous 
to  a  fall  of  RAIN  ? 

A.  Because  they  smell  the  odor  of 
plants  and  hay,  and  delight  to  snuff  in 
their  fragrance. 

Q.  Why  does  SMOKE  FALL,  when  RAIN  is  at 
hand  ? 

A.  Because  the  air  is  less  dense,  arid 
cannot  buoy  up  the  smoke  so  readily  as 
dry  and  heavy  air. 

Q.  Why  do  SWALLOWS  FLY  LOW,  when  RAIN 
is  at  hand  ? 

A.  Because  the  insects  (of  which  they 
are  in  pursuit)  have  Jled  from  the  cold, 
upper  regions  of  tJie  air,  to  the  warm  air 
near  the  earth ;  and,  as  their  food  is  low> 
the  swallows  fly  low. 

Q.     Why  do  these  INSECTS  seek  the  lower  regions 


FOUL    WEATHER.  145 

of  the  air  in   WET   weather,  more   than  in  FINE 
weather  ? 

A.  Because  (in  wet  weather)  the 
upper  regions  of  the  air  are  colder  than 
the  lower ;  and,  as  insects  enjoy  warmth, 
they  seek  it  near  the  earth. 

Q.  Why  does  a  DOWNWARD  current  of  COLD 
AIR  bring  RAIN  ? 

A.  Because  it  condenses  the  warm 
vapor;  which  (being-  condensed)  de- 
scends in  rain. 

Q.  The  proverb  says,  "  A  SINGLE  MAGPIE  in 
spring,  FOUL  WEATHER  will  bring:"  Why  is  this 
the  case  ? 

A.  Because  in  cold,  stormy  weather, 
one  magpie  alone  will  leave  its  warm, 
snug*  nest  in  search  of  food,  while  the 
other  stays  with  the  eggs,  or  young  ones; 
but  in  jine,  mild  weather  (when  their 
brood  will  not  be  injured  by  cold)  both 
the  magpies  fly  out  together. 

Q.  Why  is  it  UNLUCKY  for  ANGLERS  to  see  a 
SINGLE  MAGPIE  in  spring  ? 

A.  Because  when  magpies  fly  abroad 
singly,  the  weather  is  cold  and  stormy ; 
but,  when  both  birds  fly  out  together,  the 
weather  is  warm  and  mild,  which  is 
favorable  for  fishing. 

Q.  Why  do  SEA-GULLS  fly  about  the  SEA  in 
FINE  weather  ? 

7 


146  EFFECTS    OF    HEAT. 

A.  Because  they  live  upon  the  fishes, 
which  are  found  near  the  surface  of  the 
sea  in  fine  weather. 

Q.  Why  may  we  expect  STORMY  RAINS,  when 
SEA-GULLS  assemble  on  the  land  ? 

A.  Because  the  fishes  (on  which 
they  live)  leave  the  surface  of  the  sea  in 
stormy  weather,  and  are  beyond  the 
reach  of  the  sea-gulls ;  in  consequence 
of  which,  they  are  obliged  to  feed  on  the 
worms  and  larvae^  which  are  driven  out 
of  the  ground  at  such  times. 

Larvas,  little  grubs  and  caterpillars. 
Q.       WTiy  do  PETRELS  fly  to  the  SEA  during  a 
storm  ? 

A.  Because  they  live  upon  sea  insects, 
which  are  always  to  be  found  in  abun- 
dance about  the  spray  of  swelling  leaves. 

N.  B.  Petrels  are  birds  of  the  duck-kind,  which  live  in 
the  open  sea.  They  run  on  the  top  of  the  waves,  and  are 
called  Petrels,  or  rather  Peter-els,  from  "  St.  Peter,"  in 
allusion  to  his  walking  on  the  sea,  to  go  to  Jesus. 

Q.  Why  do  CANDLES  and  LAMPS  SPIRT,  when 
RAIN  is  at  hand  ? 

A.  Because  the  air  is  filled  with  vapor 
which  penetrates  the  wick;  where  (being 
formed  into  steam)  it  expands  suddenly, 
and  produces  a  little  explosion. 

Q.  Why  does  a  DROP  of  WATER  sometimes  ROLL 
along  a  piece  of  hot  iron,  without  leaving  the  least 
trace? 


VAPOR.  147 

A.  Because  the  bottom  of  the  drop  is 
turned  into  vapor,  which  buoys  the  drop 
up,  without  allowing*  it  to  touch  the  iron. 

Q.       Why  does  it  ROLL  1 

A.  Because  the  current  of  air  (which 
is  always  passing  over  a  heated  surface) 
drives  it  along. 

Q.  Why  does  a  LAUNDRESS  put  a  little  SALIVA 
on  a  FLAT-IRON,  to  know  if  it  be  hot  enough  ? 

A.  Because  when  the  saliva  sticks  to 
the  box,  and  is  evaporated,  she  knows  it 
is  not  sufficiently  hot ;  but,  when  it  runs 
along  the  iron,  it  is. 

Q.  Why  is  the  FLAT-IRON  HOTTER  if  the  saliva 
RUNS  ALONG  it,  than  if  it  adheres  till  it  is  evapor- 
ated ? 

A.  Because  when  the  saliva  runs 
along  the  iron,  the  heat  is  sufficient  to 
convert  the  bottom  of  the  drop  info  vapor  ; 
but,  if  the  saliva  will  not  roll,  the  iron  is 
not  sufficiently  hot  to  convert  the  bottom 
of  the  drop  into  vapor. 


CHAPTER  XIV. 

4. EVAPORATION. 

Q.       What  is  meant  by  EVAPORATION  ? 

A.     The  dissipation  of  liquid  by  its 
conversion  into  vapor. 


148  EFFECTS    OF    HEAT. 

Q.       What  EFFECTS  are  produced  by  evaporation  ? 

A.  The  liquid  vaporized  absorbs  heat 
from  the  body  whence  it  issues ;  and  the 
body  deprived  of  the  liquid  by  evapora- 
tion, loses  heat. 

Q.  If  you  WET  your  FINGER  in  your  mouth, 
and  hold  it  up  in  the  air^  why  does  it  FEEL  COLD  ? 

A.  Because  the  saliva  quickly  evap- 
orates ;  and  (as  it  evaporates)  absorbs' 
heat  from  the  finger,  making-  it  feel  cold. 

Q.  If  you  BATHE  your  TEMPLES  with  ether, 
why  does  it  allay  INFLAMMATION  and  feverish  heat  1 

A.  Because  ether  very  rapidly  evapo- 
rates ;  and  (as  it  evaporates)  absorbs  heat 
from  the  burning  head,  producing  a  sen- 
sation of  cold. 

Q.  Why  is  ETHER  better  for  this  purpose  than 
WATER? 

A.  Because  ether  requires  less  heat 
to  convert  it  into  vapor ;  in  consequence 
of  which,  it  evaporates  more  quickly. 

N.  B.    Ether  is  converted  into  vapor  with  100°  of  heat : 
"but  water  requires  212°  of  heat  to  convert  it  into  steam. 

Q.       Why  does  ETHER  very  greatly  RELIEVE  a 

SCALD  Or  BURN  ? 

A.  Because  it  evaporates  very  rapidly; 
and  (as  it  evaporates)  carries  off  the  heat 
of  the  burn. 

Q.       Why  do  we  FEEL  COLD,  when  we  have  WET 

FEET  Or  CLOTHES  ? 

A.     Because  the  wet  of  our  shoes  or 


DAMP    CLOTHES.  149 

clothes  rapidly  evaporates ;  and  (as  it 
evaporates)  absorbs  heat  from  our  body, 
which  makes  us  feel  cold. 

Q.  Why  do  WET  FEET  or  CLOTHES  give  us 
«  COLD  ?" 

A.  Because  the  evaporation  absorbs 
heat  so  abundantly  from  the  surface  of 
our  body,  that  its  temperature  is  lowered 
below  its  natural  standard;  in  conse- 
quence of  which,  health  is  injured. 

Q.  Why  is  it  DANGEROUS  to  SLEEP  in  a  DAMP 
BED? 

A.  Because  the  heat  is  continually 
absorbed  from  the  surface  of  our  body, 
to  convert  the  damp  of  the  sheets  into  va- . 
por ;  in  consequence  of  which,  our  ani- 
mal heat  is  reduced  below  the  healthy 
standard. 

Q.  Why  is  HEALTH  INJURED,  when  the  TEM- 
PERATURE of  the  BODY  is  REDUCED  below  its  natural 
standard  ? 

A.  Because  the  balance  of  the  circula- 
tion is  destroyed.  Blood  is  driven  away 
from  the  external  surface  by  the  chill, 
arid  thrown  upon  the  internal  organs, 
which  are  oppressed  by  this  increased 
load  of  blood. 

Q.  Why  do  we  not  feel  the  same  sensation  of 
cold,  if  we  throw  a  MACINTOSH  over  our  WET 
CLOTHES  ? 


150  EFFECTS    OF    HEAT. 

A.  Because  the  macintosh  (being*  air 
tight)  prevents  evaporation;  and  (as  the 
wet  canrwt  evaporate)  no  heat  is  absorbed 
from  our  bodies. 

Q.  Why  do  NOT  SAILORS  get  COLD,  who  are 
frequently  wet  all  day  with  SEA- WATER  ? 

A.  1st — Because  the  salt  of  the  sea 
retards  evaporation  ;  and  (as  the  heat  of 
their  body  is  drawn  off  gradually)  the 
sensation  of  cold  is  prevented. 

2dly — The  salt  of  the  sea  acts  as  a 
stimulant,  and  keeps  the  blood  circulat- 
ing in  the  skin. 

Q.       Why  does  SPRINKLING  a  HOT  ROOM  with 
•  water  COOL  IT  ? 

A.  Because  the  heat  of  the  room 
causes  a  rapid  evaporation  of  the  sprin- 
kled water  :  and  as  the  water  evaporates, 
it  absorbs  heat  from  the  room,  which 
cools  it. 

Q.  Why  does  WATERING  the  STREETS  and 
roads  COOL  THEM  ? 

A.  Because  they  part  with  their  heat 
to  promote  the  evaporation  of  the  water 
sprinkled  on  them. 

Q.  Why  does  a  SHOWER  of  RAIN  COOL  the  AIR 
in  summer-time  ? 

A.  Because  the  wet  earth  parts  with 
its  heat  to  promote  evaporation ;  and  when 
the  earth  is  cooled,  it  cools  the  air  also. 


EVAPORATION.  151 

Q.  Why  is  LINEN  DRIED  by  being  exposed  to 
the  WIND  ? 

A.  Because  the  wind  accelerates 
evaporation,  by  removing  the  vapor  from 
the  surface  of  tlw  wet  /men,  as  fast  as  it 
is  formed. 

Q.  Why  is  LINEN  DRIED  sooner  in  the  open 
AIR,  than  in  a  confined  room  ? 

A.  Because  the  particles  of  vapor  are 
more  rapidly  removed  from  the  surface 
of  the  linen  by  evaporation. 

Q.  Why  are,  WET  SUMMERS  generally  SUC- 
CEEDED by  COLD  WINTERS? 

A.  Because  the  great  evaporation 
(carried  on  through  the  wet  summer) 
reduces  the  temperature  of  the  earth  lower 
than  usual,  and  produces  cold. 

Q.  Why  is  THIS  COUNTRY  WARMER  and  the 
winters  less  severe  than  formerly  ? 

A.  Because  it  is  better  drained  and 
better  cultivated. 

Q.       Why  does  DRAINING  land  promote  WARMTH  ? 

A.  Because  it  diminishes  evaporation  ; 
in  consequence  of  which,  less  heat  is  ab- 
stracted from  the  earth. 

Q.  Why  does  CULTIVATION  increase  the 
WARMTH  of  a  country  ? 

A.  1st — Because  hedges  and  belts  of 
trees  are  multiplied : 

2dly — The  land  is  better  drained :  and 


152  EFFECTS    OF    HEAT. 

3dly  — The  vast  forests  are  cut  down. 

Q.  Why  do  HEDGES  and  BELTS  of  TREES  pro- 
mote WARMTH  ? 

A.  Because  they  retard  evaporation, 
by  keeping-  off  the  wind. 

Q.  If  belts  of  trees  promote  WARMTH,  why  do 
FORESTS  produce  COLD  ? 

A.  1st — Because  they  detain  and 
condense  the  passing  clouds ; 

2dly — They  prevent  the  access  of 
both  wind  and  sun  ; 

3dly — The  soil  of  forests  is  always 
covered  with  long,  damp  grass,  rotting 
leaves,  and  thick  brushwood  ;  and 

4thly — In  every  forest  there  are  al- 
ways many  hollows  fall  of  stagnant 
water. 

Q.  Why  do  LONG  GRASS  and  ROTTING  LEAVES 
promote  COLD  ? 

A.  Because  they  are  always  damp  ; 
and  evaporation,  which  they  promote,  is 
constantly  absorbing  heat  from  the  earth 
beneath. 

Q.  Why  are  FRANCE  and  GERMANY  WARMER 
now,  than  when  the  vine  would  not  ripen  there  ? 

A.  Chiefly  because  their  vast  forests 
have  been  cut  doivn;  and  the  soil  is  bet- 
ter drained  and  cultivated. 

Q.  What  becomes  of  the  WATER  of  PONDS  and 
TUBS  in  summer-time  ? 


EVAPORATION.  153 

A.  Ponds  and  tubs  are  often  left  dry 
in  summer-time,  because  their  water  is 
evaporated  by  the  air. 

Q.  How  is  this  EVAPORATION  PRODUCED  and 
carried  on  ? 

A.  The  heat  of  the  air  changes  the 
surface  of  the  water  into  vapor,  which 
(blending  with  the  air)  is  soon  wafted 
away ;  and  similar  evaporation  is  repeat- 
edly produced,  till  the  pond  or  tub  is 
left  quite  dry. 

Q.       Why  are  the  WHEELS  of  some  machines 

kept  CONSTANTLY  WET  With  WATER  ? 

A.  To  carry  off  (by  evaporation)  the 
heat  which  arises  from  the  rapid  motion 
of  the  wheels. 

Q.       Why  is  MOULD  HARDENED  by  the  SUN  ? 

A.  Because  the  moisture  of  the 
mould  is  exhaled  by  evaporation ;  and, 
as  the  earthy  particles  are  brought  closer 
together,  the  mass  becomes  more  solid. 

Q.  Show  the  WISDOM  of  GOD  in  this  arrange- 
ment. 

A.  If  the  soil  did  not  become  crusty 
and  hard  in  dry  weather,  the  heat  and 
drought  would  penetrate  the  soil,  and  kill 
both  seeds  and  roots. 

Q.  Why  is  TEA  cooled  FASTER  in  a  SAUCER. 
than  in  a  cup  ? 

A.     Because  evaporation  is  increased 

7* 


154  EFFECTS    OF   HEAT. 

by  increasing  the  surface ;  and,  as  tea  in 
a  saucer  presents  a  larger  surface  to  the 
air,  its  heat  is  more  rapidly  carried  off 
by  evaporation. 

(The  subject  <*?  "  convection"  will  be  treated  of  in  a  fu- 
ture chapter;  it  would  scarcely  be  understood  in  this 
place.  See  p.  213.) 

Q.       Why  is  not  the  VAPOR  of  the  SEA  SALT  ? 
A.     Because  the  salt  is  always  left 
behind,  in  the  process  of  evaporation. 

Q.  What  is  that  WHITE  CRUST,  which  appears 
(in  hot  weather)  upon  CLOTHES  wetted  by  sea  water  ? 

A.  The  salt  of  the  water,  left  on  the 
clothes  by  evaporation. 

Q.  Why  does  this  WHITE  CRUST  always  DIS- 
APPEAR in  WET  weather? 

A.  Because  the  moisture  of  tlie  air 
dissolves  the  salt;  in  consequence  of 
which,  it  is  no  longer  visible. 

Q.  Why  should  NOT  persons,  who  take  violent 
exercise,  WEAR  very  THICK  CLOTHING  ? 

A.  Because  it  prevents  the  perspira- 
tion from  evaporating*.  When  the  heat 
of  the  body  is  increased  by  exercise,  per- 
spiration reduces  the  heat  (by  evapora- 
tion) to  a  healthy  standard ;  as  thick 
clothing  prevents  this  evaporation,  it  is 
injurious  to  health. 


CONDUCTION.  155 

COMMUNICATION    OF    HEAT. 
CHAPTER  XV. 
1 — CONDUCTION. 

Q.         HOW  is  HEAT  COMMUNICATED  /TOM  0716  body 

to  another  ? 

A.  1.— By  Conduction.  2.— By  Ab- 
sorption. 3. — By  Reflection.  4 — By 
Radiation.  And  5. — By  Convection. 

»Q.       What  is  meant  by  CONDUCTION  of  heat  ? 
A.     Heat    communicated    from    one 
body  to  another  by  actual  contact. 

Q.  Why  does  a  PIECE  of  WOOD  (blazing  at 
ONE  end)  NOT  feel  HOT  at  the  OTHER? 

A.  Because  ivood  is  so  bad  a  conduct- 
or, that  heat  does  not  traverse  freely 
through  it ;  hence,  though  one  end  of 
a  stick  be  blazing-  the  other  end  may  be 
quite  cold. 

Q.  Why  do  SOME  THINGS  feel  COLDER  than 
others  ? 

A.  Principally  because  they  are  bet- 
ter conductors ;  and  draw  off  heat  from 
our  body  much  faster. 

Q.       What  are  the  BEST  CONDUCTORS  of  HEAT  ? 

A.  Dense,  solid  bodies,  such  as  metal 
and  stone. 


156  COMMUNICATION    OP    HEAT. 

Q.  Which  METALS  are  the  most  RAPID  CONDUCT- 
ORS 0/*HEAT? 

A.  The  best  conductors  of  heat  are 
1.  gold,  2.  silver,  3.  copper: 

The  next  best  are  4.  plat'inum,  5.  iron, 
6.  zinc,  7.  tin.  Lead  is  a  very  inferior 
conductor  to  any  of  the  preceding  metals. 

Q.       What  are  the  WORST  CONDUCTORS  O/*HEAT  ? 

A.  All  light  and  porous  bodies;  such 
as  hair,  fur,  wool,  charcoal,  and  so  on. 

Two  of  the  worst  conductors  known  are  hare's  fur  and 
eider  down ; — the  two  next  worst  are  beaver's  fur  and  raw 
silk ; — then  wood  and  lamp-black ; — then  cotton  and  fine 
lint ;— -then  charcoal,  wood  ashes,  &c. 

Q.       Why  are  COOKING  VESSELS  often  furnished 

With  WOODEN  HANDLES? 

A.  Because  wood  is  not  a  good  con- 
ductor, like  metal ;  and,  therefore,  wooden 
handles  prevent  the  heat  of  the  vessel 
from  rushing  into  our  hands,  to  burn 
them. 

Q.  Why  is  the  HANDLE  of  a  METAL  TEA-POT 
made  of  WOOD  ? 

A.  Because  wood  is  a  bad  conductor  ; 
therefore,  the  heat  of  the  boiling  water 
is  not  so  quickly  conveyed  to  our  hand  by  a 
wooden  handle,  as  by  one  made  of  metal. 

Q.  Why  would  a  METAL  HANDLE  BURN  the 
HAND  of  the  tea-maker  ? 

A.  Because  metal  is  an  excellent  con- 
ductor ;  therefore,  the  heat  of  boiling  wa- 


KETTLE-HOLDERS.  157 

ter  would  rush  so  quickly  into  the  metal 
handle,  that  it  would  burn  our  hand. 

Q.'  Prove  that  a  METAL  HANDLE  would  be  HOT- 
TER than  a  WOODEN  ONE. 

A.  If  we  touch  the  metal  collar  into 
which  the  wooden  handle  is  fixed,  we 
shall  find  that  the  wooden  handle  feels 
cold,  but  the  metal  collar  intensely  hot. 

Q.       Why  do  persons  use  paper  or  WOOLLEN 

KETTLE-HOLDERS? 

A.  Because  paper  and  woollen  are 
both  very  bad  conductors  of  heat ;  in  con- 
sequence of  which,  the  heat  of  the  kettle 
does  not  readily  pass  through  them  to  the 
hand. 

Q.  Does  the  heat  of  the  boiling  kettle  NEVER 
get  through  the  woollen  or  paper  kettle-holder  ? 

A.  Yes ;  but  though  the  kettle-holder 
became  as  hot  as  the  kettle  itself,  it 
would  never  feel  so  hot. 

Q.  Why  would  not  the  kettle-holder  FEEL  so  hot 
as  the  kettle,  when  both  are  of  the  same  temperature  ? 

A.  Because  it  is  a  very  bad  conduct- 
or, and  disposes  of  its  heat  too  slowly  to 
be  perceptible ;  but  metal  (being  an  ex- 
cellent conductor)  disposes  of  its  heat  so 
quickly \  that  the  sudden  influx  is  painful. 

Q.  Why  does  HOT  METAL  FEEL  MORE  intensely 
WARM  than  HOT  WOOL  ? 

A.     Because  metal  gives  out  a  much 


158  COMMUNICATION    OP    HEAT. 

greater  quantity  of  heat  in  the  same  space 
of  time ;  and  the  influx  of  heat  is,  con- 
sequently, more  perceptible. 

Q.  Why  does  MONEY  in  our  pocket  feel  very 
HOT  when  we  stand  BEFORE  a  FIRE  1 

A.  Because  metal  is  an  excellent  con- 
ductor, and  becomes  rapidly  heated. 
For  the  same  reason,  it  becomes  rapidly 
cold,  whenever  it  comes  in  contact  with 
a  body  colder  than  itself. 

Q.       Why  does  a   PUMP-HANDLE  feel  intensely 

COLD  in  WINTER  ? 

A.  Because  it  is  an  excellent  conduct- 
or, and  draws  off  the  heat  of  our  hand 
so  rapidly,  that  the  sudden  loss  produces 
a  sensation  of  intense  coldness. 

Q.  Is  the  iron  HANDLE  of  the  pump  really 
COLDER  than  the  wooden  PUMP  itself? 

A.  No ;  every  inanimate  substance 
(exposed  to  the  same  temperature)  pos- 
sesses in  reality  th6  same  degree  of  heat. 

Q.  Why  does  the  IRON  HANDLE  seem  so  MUCH 
COLDER  than  the  WOODEN  PUMP  ? 

A.  Merely  because  the  iron  is  a  bet- 
ter conductor ;  and,  therefore,  draws  off 
the  heat  from  our  hand  more  rapidly 
than  wood  does. 

Q.  Why  does  a  STONE  or  marble  HEARTH  feel 
to  the  feet  COLDER  than  a  CARPET  or  hearth-rug? 

A.     Because  stone  and  marble  are  good 


CARPETS — STONES.  159 

conductors ;    but    woollen   carpets    and 
hearth-rugs  are  very  bad  conductors. 
Q.      How  does  the  STONE  HEARTH  make  our 

FEET  COLD  ? 

A.  As  soon  as  the  hearth-stone  has 
absorbed  a  portion  of  heat  from  our  foot, 
it  instantly  disposes  of  it,  and  calls  for  a 
fresh  supply ;  till  the  hearth-stone  has  be- 
come of  the  same  temperature  as  the  foot 
placed  upon  it. 

Q.  Do  not  also  the  woollen  CARPET  and  HEARTH- 
RUG conduct  heat  from  the  human  body? 

A.  Yes  ;  but  being-  very  bad  conduct- 
ors, they  convey  the  heat  away  so  slow- 
ly, that  the  loss  is  scarcely  perceptible. 

Q.      Is  the  COLD   HEARTH-STONE  in  reality  of 

the  SAME  TEMPERATURE  as  the  WARM  CARPET  ? 

A.  Yes ;  every  thing  in  the  room  is 
really  of  one  temperature  ;  but  some 
things  feel  colder  than  others,  because 
they  are  better  conductors. 

Q.  How  LONG  will  the  hearth-stone  feel  cold  to 
the  feet  resting  on  it  ? 

A.  Till  the  feet  and  the  hearth-stone 
are  both  of  the  same  temperature  ;  and 
then  the  sensation  of  cold  in  the  hearth- 
stone will  go  off. 

Q.  Why  would  not  the  HEARTH-STONE  feel 
COLD,  when  it  is  of  the  SAME  temperature  as  our 
FEET? 


160  COMMUNICATION    OP   HEAT, 

A.  Because  the  heat  would  no  long- 
er rush  out  of  our  feet  into  the  hearth- 
stone, in  order  to  produce  equilibrium, 

Q.  Why  does  the  HEARTH-STONE  (when  the  fire 
is  lighted)  feel  HOTTER  than  the  HEARTH-RUG  ? 

A.  Because  the  hearth-stone  is  an 
excellent  conductor,  and  parts  with  its 
heat  very  readily  ;  but  the  woollen  hearth- 
rug* (being-  a  bad  conductor)  parts  with 
its  heat  very  reluctantly. 

Q.  Why  does  PARTING  with  HEAT  RAPIDLY 
make  the  H  EARTH-STONE  feel  WARM? 

A.  Because  the  rapid  influx  of  heat 
raises  the  temperature  of  our  body  so  sud- 
denly, that  we  cannot  help  perceiving  the 
increase. 

Q.  Why  does  the  non-conducting  power  of  the 
HEARTH-RUG  prevent  its  feeling  so  HOT  as  it  really  is? 

A.  Because  it  parts  with  its  heat  so 
slowly  and  gradually,  that  we  scarcely 
perceive  its  transmission  into  our  feet. 

Q.  When  we  plunge  our  HANDS  into  a  basin 
of  WATER  why  does  it  produce  a  sensation  of  COLD  ? 

A.  Because  water  is  a  better  conduct- 
or  than  air;  and,  as  it  draws  off  the 
heat  from  our  hands  more  rapidly,  it  feels 
colder. 

Q.  Why  does  the  CONDUCTING  power  of  water 
make  it  feel  COLDER  than  AIR  ? 

A.     Because  it  abstracts  heat  from  our 


WATER.  161 

hands  so  rapidly,  that  we  feel  its  loss; 
but  the  air  abstracts  heat  so  very  slowly, 
that  its  gradual  loss  is  hardly  perceptible. 

Q.      Is  water  a  GOOD  CONDUCTOR  of  heat  ? 

A.  No  ;  no  liquid  is  a  good  conductor 
of  heat ;  but  yet  water  is  a  much  better 
conductor  than  air. 

Q.  Why  is  WATER  a  BETTER  CONDUCTOR  of 
heat  than  AIR  1 

A.  Because  it  is  less  subtile ;  and  the 
conducting  power  of  any  substance  de- 
pends upon  its  solidity,  or  the  closeness 
of  its  particles. 

Q.  How  do  you  know  that  WATER  is  NOT  a 
GOOD  CONDUCTOR  of  heat  ? 

A.  Because  it  may  be  made  to  boil  at 
its  surface,  without  imparting  sufficient 
heat  to  melt  ice  a  quarter  of  an  inch  below 
the  surface. 

Q.  Why  cure,  NOT  LIQUIDS  GOOD  CONDUCTORS 
of  heat  ? 

A.  Because  the  heat  (which  should 
be  transmitted)  produces  evaporation,  and 
flies  off  in  the  vapor.  , 

Q.  Why  does  a  POKER  (resting  on  a  fender) 
feel  COLDER  than  the  HEARTH-RUG,  which  is  further 
off  the  fire? 

A.  Because  the  poker  is  an  excellent 
conductor,  and  draws  heat  from  the  hand 
much  more  rapidly  than  the  woollen 


162  COMMUNICATION    OP    HEAT. 

hearth-rug-,  which  is  a  very  bad  conductor: 
though  both,  therefore,  are  equally  warm, 
the  poker  seems  to  be  the  colder.  (See 
also  p.  173.) 

Q.  Why  are  HOT  BRICKS  (wrapped  in  cloth) 
employed  in  cold  weather  to  KEEP  the  FEET  WARM  ? 

A.  Because  bricks  are  bad  conductors 
of  heat,  and  cloth  or  flannel  still  worse : 
in  consequence  of  which,  a  hot  brick 
(wrapped  in  flannel)  will  retain  its  heat 
a  very  long  time. 

Q.  Why  is  a  TIN  PAN  (filled  with  HOT  WATER) 
employed  as  a  FOOT- WARMER  ? 

A.  Because  polished  tin  (being1  a  bad 
radiator  of  heat)  keeps  hot  a  very  long 
time ;  arid  warms  the  feet  resting-  upon  it. 

Q.  What  is  meant  by  being  a  "  bad  RADIATOR 
of  heat .?" 

A.  To  radiate  heat  is  to  throw  off 
heat  by  rays,  as  the  sun ;  a  polished  tin 
pan  does  not  throw  off  the  heat  of  boiling 
water  from  its  surface,  but  keeps  it  in. 

Q.       Why  are  TIN  FOOT-WARMERS  covered  with 

FLANNEL  ? 

A.  1st — That  the  polish  of  the  tin 
may  not  be  injured : 

2dly — Because  the  flannel  (being*  a 
very  bad  conductor)  helps  to  keep  the  tin 
hot  longer :  and 


FOOT-WARMERS — STOVES.  163 

3dly — Lest  the  conducting*  surface  of 
the  tin  should  feel  painfully  hot. 

Q.  What  disadvantage  would  it  be,  if  the  POL- 
ISH  of  the  tin  were  injured  ? 

A.  If  the  tin  foot- warmer  were  to 
lose  its  polish,  it  would  get  cold  in  a  much 
shorter  time. 

Q.  Why  would  the  tin  foot-warmer  get  COLD 
SOONER,  if  the  POLISH  were  INJURED  ? 

A.  Because  polished  tin  throws  off  its 
heat  very  slowly;  but  dull,  scratched, 
painted,  or  dirty  tin,  throws  off  its  heat 
very  quickly. 

Q.  Why  are  FURNACES  and  stoves  (where 
much  HEAT  is  required)  built  of  porous  BRICK  ? 

A.  Because  bricks  are  bad  con- 
ductors, and  prevent  the  escape  of  heat  ; 
in  consequence  of  which,  they  are  em- 
ployed where  great  heat  is  required. 

Q.  Why  are  FURNACE  DOORS,  fyc.,  frequently 
COVERED  with  a  paste  of  CLAY  and  SAND? 

A.  Because  this  paste  is  a  very  bad 
conductor  of  heat;  and,  therefore,  pre- 
vents the  escape  of  heat  from  the  furnace. 

Q.  If  a  stove  be  placed  in  the  MIDDLE  of  a  room 
should  it  be  made  of  bricks  or  IRON  ? 

A.  A  stove  in  the  middle  of  a  room 
should  be  made  of  iron ;  because  iron 
is  an  excellent  conductor,  and  rapidly 
communicates  heat  to  the  air  around. 


164  COMMUNICATION    OF    HEAT. 

Q.  Why  does  the  Bible  say,  that  God  "  giveth 
BNOW  like  WOOL  ?" 

A.  Because  snow  (being-  a  very  bad 
conductor  of  lieat)  protects  vegetables 
and  seeds  from  the  frost  and  cold. 

Q.  How  does  the  non-conducting  power  of  SNOW 
PROTECT  VEGETABLES  from  the  FROST  and  cold? 

A.  It  prevents  the  heal  of  the  earth 
from  being-  drawn  off  by  the  cold  air 
which  rests  upon  it. 

Q.  Why  are  WOOLLENS  and  FURS  used  for 
CLOTHING  in  COLD  weather  ? 

A.  Because  they  are  very  bad  con- 
ductors of  heat;  and,  therefore,  prevent 
the  warmth  of  the  body  from  being  drawn 
off  by  the  cold  air. 

Q.  Do  not  woollens  and  furs  actually  IMPART 
heat  to  the  body  ?  ^ 

A.  No ;  they  merely  prevent  the  heat 
of  the  body  from  escaping. 

Q.  Where  would  the  heat  ESCAPE  to,  if  the 
body  were  NOT  wrapped  in  wool  or  fur  ? 

A.  The  heat  of  the  body  would  fly 
off  into  the  air;  for  the  cold  air  (coming 
in  contact  with  our  body)  would  gi*adu- 
ally  draw  away  its  heat,  till  it  was  as 
cold  as  the  air  itself. 

Q.  What  then  is  the  PRINCIPAL  USE  of  CLOTH- 
ING in  winter-time  ? 

A.  1st — To  prevent  the  animal  heat 
from  escaping  too  freely  ;  and 


AIR.  165 

2dly — To  protect  the  body  from  the 
external  air  (or  wind),  which  would 
carry  away  its  heat  too  rapidly. 

Q.  Why  are  BEASTS  COVERED  with  FUR,  HAIR 
or  WOOL  ? 

A.  Because  fur,  hair  and  wool,  are 
very  slow  conductors  of  heat;  arid  (as 
dumb  animals  cannot  be  clad,  like  human 
being's)  God  has  given  them  a  robe  of 
hair  or  wool,  to  keep  them  warm. 

Q.       Why  are  BIRDS   covered   with   DOWN  or 

FEATHERS  ? 

A.  Because  down  and  feathers  are 
very  bad  conductors  of  heat;  and  (as 
birds  cannot  be  clad,  like  human  beings) 
God  has  given  them  a  robe  of  feathers, 
to  keep  them  warm. 

Q.  Why  are  WOOL,  FUR,  HAIR,  and  FEATHERS, 
such  SLOW  CONDUCTORS  of  heat  ? 

A.  Because  a  great  quantity  of  air 
lurks  entangled  between  the  fibres;  and 
air  is  a  very  bad  conductor  of  heat. 

The  warmest  clothing  is  that  which  fits  the  body  very 
loosely  in  every  part  except  at  the  extremities:  Because 
more  hot  air  will  be  confined  by  a  loose  garment  than  by 
one  which  fits  the  body  tightly. 

Q.  If  AIR  be  a  BAD  CONDUCTOR  of  heat,  why 
should  we  not  feel  as  warm  WITHOUT  clothing,  as 
when  we  are  wrapped  in  wool  and  fur  ? 

A.  Because  the  air  (which  is  cooler 
than  our  body)  is  never  at  rest;  and 


166  COMMUNICATION    OF    HEAT. 

every  fresh  particle  of  air  draws  off  a 
fresh  portion  of  heat. 

Q.  How  does  the  ceaseless  CHANGE  of  air  tend 
to  DECREASE  the  WARMTH  of  a  naked  body? 

A.  Thus : — the  air  (which  cases  the 
body)  absorbs  as  much  heat  from  it  as 
it  can,  while  it  remains  in  contact ;  being 
then  blown  away,  it  makes  room  for  a 
fresh  coat  of  'air ',  which  absorbs  more  heat. 

Q.  Does  the  ATR  which  encases  a  naked  body 
become  (by  contact)  as  WARM  as  the  BODY  itself? 

A.  It  would  do  so,  if  it  remained 
motionless ;  but,  as  it  remains  only  a  very 
short  time,  it  absorbs  as  much  heat  as  it 
can  in  the  time,  and  passes  on. 

Q.  Why  do  we  feel  COLDER  in  WINDY  WEA- 
THER than  in  a  CALM  day  ? 

A.  Because  the  particles  of  air  pass 
over  us  more  rapidly ;  pnd  every  fresh 
particle  takes  from  us  some  portion  of 
heat. 

Q.      Show  the  wisdom  of  God  in  making  the 

AIR  a  BAD  CONDUCTOR. 

A.  If  air  were  a  good  conductor  (like 
iron  and  stone)  heat  would  be  drawn  so 
rapidly  from  our  body,  that  we  should  be 
chilled  to  death.  Similar  evils  would  be 
felt  also  by  all  the  animal  and  vegetable 
world. 

Q.      Does  not  the  bad  conducting  power  of  air 


STALE    EGG — FANNING.  167 

enable  persons  to  judge  whether  an  EGG  be  NEW  0r 
STALE  ? 

A.  Yes ;  touch  the  larger  end  of  the 
shell  with  your  tongue  ;  if  it  feels  warm, 
the  egg  is  stale ;  if  not,  it  is  new-laid. 

Q.  Why  will  the  SHELL  of  a  STALE  EGG  feel 
WARM  to  the  tongue  ? 

A.  Because  the  thick  end  of  an  egg 
contains  a  small  quantity  of  air  (between 
the  shell  and  the  white)  ;  when  the  egg 
is  stale  the  white  shrinks,  and  the  con- 
fined air  accordingly  expands. 

Q.  Why  does  the  expansion  of  air  (at  the  end 
of 'an  egg)  make  it  feel  WARM  to  the  tongue  ? 

A.  Because  air  is  a  very  bad  conduct- 
or, and  the  more  air  an  egg  contains, 
the  less  heat  will  be  drawn  from  the  tongue 
when  it  touches  the  shell. 

Q.  Why  will  a  NEW-LAID  egg  feel  COLDER  to 
the  tongue  at  the  thick  end  than  a  stale  one  ? 

A.  Because  it  contains  more  white 
ancl  less  air ;  and  as  the  white  of  an  egg 
is  a  better  conductor  than  air,  the  heat 
of  the  tongue  will  be  drawn  offmorera- 
pidly,  and  the  egg  feel  colder. 

Q.  Why  does  FANNING  the  face  in  summer 
make  it  COOL  ? 

A.  Because  the  fan  puts  the  air  in 
motion,  and  makes  it  pass  more  rapidly 
over  the  face ;  and  (as  the  temperature  of 


168  COMMUNICATION    OP   HEAT. 

the  air  is  always  lower  than  that  of  the 
human  face)  each  puff  of  air  carries  off 
some  portion  of  its  heat. 

Q.      Does  FANNING  make  the  AIR  itself  COOLER  ? 
A.     No  ;  fanning  makes  the  air  Iwtter 
and  Jwtter. 

Q.  How  does  FANNING  the  face  increase  the 
HEAT  of  the  air  ? 

A.  By  driving-  the  air  more  rapidly 
over  the  human  body,  and  causing-  it, 
consequently,  to  absorb  more  Iwat. 

Q.  If  fanning  makes  the  AIR  HOTTER,  why  can 
it  make  a  PERSON  feel  COOLER  ? 

A.  Because  it  takes  the  heat  out -of 
the  face,  and  gives  it  to  the  air. 

Q.       Why  is  BROTH  COOLED  by  BLOWING  it  ? 

A.  Because  the  breath  causes  a  rap- 
id change  of  air  to  pass  over  the  broth ; 
and  (as  the  air  is  colder  than  the  broth) 
it  continually  absorbs  heat  from  it,  and 
makes  it  cooler  and  cooler. 

Q.  Would  not  the  air  absorb  heat  from  the 
broth  just  as  well  WITHOUT  BLOWING? 

A.  No  ;  air  is  a  very  bad  conductor  ; 
unless,  therefore,  the  change  be  rapid,  the 
air  nearest  the  surface  of  the  broth  would 
soon  become  as  Iwt  as  the  broth  itself. 

Q.  Would  not  hot  air  PART  with  its  heat  in- 
stantly to  the  CIRCUMJACENT  air  ? 

A.     No ;  not  instantly.     Air  is  so  bad 


WIND.  169 

a  conductor,  that  it  parts  with  its  heat 
very  slowly:  unless,  therefore,  the  air  be 
kept  in  continual  motion,  it  would  cool 
the  broil i  very  slowly  indeed. 

Q.       Why  does  WIND  generally  feel  COOL  ? 

A.  Because  it  drives  the  air  more 
rapidly  over  our  body  ;  and  this  rapid 
change  of  air  draws  off  a  large  quantity 
of  heat 

Q.  Why  does  AIR  ABSORB  heat  more  QUICKLY 
by  being  set  in  MOTION  ? 

A.  Because  every  fresh  gust  of  air 
absorbs  a  fresli  portion  of  heat ;  and  the 
more  rapid  the  succession  of  gusts,  the 
greater  will  be  the  quantity  of  heat  ab- 
sorbed. 

Q.  If  the  AIR  were  HOTTER  than  our  body 
vsould  the  WIND  feel  COOL  ? 

A.  No  ;  the  air  would  feel  insuffera- 
bly hot,  if  it  were  /totter  than  our  body. 

Q.  Why  would  the  AIR  feel  INTENSELY  HOT,  if 
it  were  WARMER  than  our  BODY  ? 

A.  Because  it  would  add  to  the  heat 
of  our  body,  instead  of  diminishing  it. 

Q.  Is  the  AIR  EVER  as  HOT  as  the  human 
BODY? 

A.  Not  in  this  country :  in  the  hot- 
test, summer's  day,  the  air  is  at  least  10 
or  12  degrees  cooler  than  the  human  body. 

Q.      Is  the  EARTH  a  good  conductor  of  heat  f 
8 


170  COMMUNICATION    OF    HEAT. 

A.  No  ;  the  earth  is  a  very  bad  con- 
ductor of  heat* 

Q.       Why  is  the  EARTH  a  BAD  conductor  of  heat  ? 

A.  Because  its  particles  are  not  con- 
tinuous :  and  the  power  of  conducting 
heat  depends  upon  the  continuity  of 
matter. 

Q.  Why  is  the  earth  (BELOW  the  SURFACE) 
WARMER  in  WINTER  than  tJie  surface  itself? 

A.  Because  the  earth  is  a  bad  con- 
ductor of  heat;  and,  therefore,  (although 
the  ground  be  frozen,)  the  frost  never 
penetrates  more  than  a  few  inches  below 
the  surface. 

Q.  Why  is  the  earth  (BELOW  the  SURFACE) 
COOLER  in  SUMMER  than  the  surface  itself? 

A.  Because  the  earth  is  a  bad  con- 
ductor of  heat ;  and,  therefore,  (although 
the  surface  be  scorched  with  the  burning 
sun,)  the  intense  heat  cannot  penetrate 
to  the  roots  of  the  plants  and  trees. 

Q.      Show  the  WISDOM  of  G-OD  in  making  the 

EARTH  a  BAD  CONDUCTOR  ? 

A.  If  the  heat  and  cold  could  pene- 
trate the  earth  (as  freely  as  the  heat  of 
a  fire  penetrates  iron),  the  springs 
would  be  dried  up  in  summer,  and  fro- 
zen in  winter ;  and  all  vegetation  would 
perish. 


SHADE    COOL.  171 

Q.  Why  is  WATER  from  a  SPRING  always 
COOL  even  in  SUMMER  ? 

A.  Because  the  earth  is  so  bad  a  con- 
ductor, that  the  burning*  rays  of  the  sun 
can  penetrate  only  a  few  inches  below 
the  surface  ;  in  consequence  of  which, 
the  springs  of  water  are  not  affected  by 
the  heat  of  summer. 

Q.  Why  is  it  COOL  under  a  SHADY  tree  in  a 
hot  summers  day  ? 

A.  1st — Because  the  overhanging-  fo- 
liage screens  offtlie  rays  of  the  sun  : 

2dly — As  the  rays  of  the  sun  are  ward- 
ed off,  the  air  (beneath  the  tree)  is  not 
heated  by  the  reflection  of  the  earth :  and 

3dly — The  leaves  of  the  trees,  being 
non-conductors,  allow  no  heat  to  pene- 
trate them. 

Q.       Why  do  the  LAPLANDERS  wear  SKINS  with 

the  FUR  INWARDS? 

A.  Because  the  dry  skin  prevents  the 
wind  from  penetrating  to  their  body ; 
and  the  air  (between  the  hairs  of  the  fur) 
soon  becomes  heated  by  the  body:  in 
consequence  of  which,  the  Laplander  in 
his  fur  is  clad  in  a  case  of  hot  air,  imper- 
vious to  the  cold  and  wind. 

Q.  Why  does  a  LINEN  SHIRT  feel  COLDER  than 
a  COTTON  ONE  ? 

A.     Because   linen  is  a  much  better 


172  COMMUNICATION    OF    HEAT. 

conductor  than  cotton ;  and,  therefore, 
(as  soon  as  it  touches  the  body)  it  draws 
away  the  heat  more  rapidly,  and  pro- 
duces a  greater  sensation  of  cold. 

Q.  Why  is  the  FACE  COOLED  by  wiping  the 
temples  with  a  fine  CAMBRIC  HANDKERCHIEF  ? 

A.  Because  the  fine  fibres  of  the 
cambric  have  a  strong  capillary  attraction 
for  moisture,  and  are  excellent  conductors 
of  heat:  in  consequence  of  which,  the 
moisture  and  heat  are  abstracted  from 
the  face  by  the  cambric,  and  a  sensation 
of  coolness  produced. 

"  Capillary  attraction,"  i.  e.,  the  attraction  of  a  thread  or 
hair.  The  wick  of  a  candle  is  wet  with  grease,  because 
the  melted  tallow  runs  up  the  cotton  from  capillary  at- 
traction. 

Q.  Why  would  not  a  COTTON  handlcerchief  do 
as  well  ? 

A.  Because  the  coarse  fibres  of  cot- 
ton have  very  little  capillary  attraction, 
and  are  very  bad  conductors ;  in  conse- 
quence of  which,  the  heat  of  the  face 
would  be  increased  (rather  than  dimin- 
ished} by  the  use  of  a  cotton  handker- 
chief. 


ABSORPTION.  173 

CHAPTER   XVI. 
2. — ABSORPTION  OF  HEAT. 

Q.  What  is  the  difference  between  CONDUCTING 
heat,  and  ABSORBING  heat  ? 

A.  To  conduct  heat  is  to  transmit  it 
from  one  body  to  another  through  a  con- 
ducting medium.  To  absorb  heat  is  to 
suck  it  up,  as  a  sponge  sucks  up  water. 

Q.       Give  me  an  example. 

A.  Black  cloth  absorbs,  but  does  not 
conduct  heat ;  thus,  if  black  cloth  be  laid 
in  the  sun,  it  will  absorb  the  rays  very 
rapidly  ;  but  if  one  end  of  the  black  cloth 
be  made  hot,  it  would  not  conduct  the 
heat  to  the  other  end. 

Q.  Are  good  CONDUCTORS  of  heat  good  AB- 
SORBERS also  ? 

A.  No ;  every  good  conductor  of  heat 
is  a  bad  absorber  of  it ;  and  no  good  ab- 
sorber of  heat  can  be  a  good  conductor 
also. 

Q.      Is  IRON  a  good  ABSORBER  of  heat  ? 

A.  No  ;  iron  is  a  good  conductor,  but 
a  very  bad  absorber  of  heat. 

Q.  Why  do  the  FIRE-IRONS  (which  lie  upon  a 
FENDER)  remain  COLD,  although  they  are  before  a 
good  fire  ? 

A.     Because  they  are  bad  absorbers  of 


174  COMMUNICATION    OP    HEAT. 

heat;  in  consequence  of  which,  they 
remain  cold,  unless  they  come  in  contact 
with  the  stove  or  fire. 

Q.  Why  are  the  FIRE-IRONS  intensely  HOT, 
when  they  REST  AGAINST  the  STOVE  which  contains 
a  good  fire  ? 

A.  Because  they  are  excellent  conduct- 
ors ofheat,  and  draw  it  rapidly  from  the 
stove  with  which  they  are  in  contact. 

Q.  Why  does  a  KETTLE  boil  faster,  when  the 
bottom  and  back  are  COVERED  with  SOOT  1 

A.  Because  the  black  soot  absorbs 
heat  very  quickly  from  the  fire,  and  the 
metal  conducts  it  to  the  water. 

Q.  Why  will  not  a  NEW  KETTLE  boil  so  fast 
as  an  OLD  one  ? 

A.  Because  the  bottom  and  sides  of  a 
new  kettle  are  clean  and  bright :  but  in 
an  old  kettle  they  are  covered  with  soot. 

Q.  Why  will  a  KETTLE  be  SLOWER  BOILING  if 
the  BOTTOM  and  BACK  are  CLEAN  and  bright  ? 

A.  Because  bright  metal  does  not  ab- 
sorb heat,  but  reflects  it ;  and  (as  the 
heat  is  thrown  off  from  the  surface  of 
bright  metal  by  reflection)  therefore,  a 
new  kettle  takes  a  longer  time  to  boil. 

Reflects  heat,  i.  e.,  throws  it  off. 

Q.  Why  do  we  wear  WHITE  LINEN  and  a 
BLACK  outer  DRESS,  if  we  want  to  be  warm  ? 

A.     Because    the    black    outer  dress 


COLORS.  175 

quickly  absorbs  heat  from  the  sun  ;  and 
the  white  linen  (being-  a  bad  absorbent) 
abstracts  no  heat  from  the  warm  body. 

Q.  Why  do  persons  WEAR  WHITE  dresses  in 
SUMMER  time  ? 

A.  Because  white  throws  off  the  heat 
of  the  sun  by  reflection,  and  is  a  very  bad 
absorbent  of  heat;  in  consequence  of 
which,  white  dresses  never  become  so 
hot  from  the  scorching  sun  as  dark  co- 
lors do. 

Q.  Why  do  NOT  persons  WEAR  WHITE  dresses 
in  WINTER  time  ? 

A.  Because  ivhite  will  not  absorb  heaty 
like  black  and  other  dark  colors;  and, 
therefore,  white  dresses  are  not  so  ivarm 
as  dark  ones. 

Q.       What  COLORS  are  WARMEST  for  dresses? 

A.  For  outside  garments  black  is  the 
warmest,  and  then  such  colors  as  ap- 
proach nearest  to  black,  (as  dark  blue 
and  green.)  White  is  the  coldest  color 
for  external  clothing*. 

Q.  Why  are  DARK  COLORS  (for  external  wear) 
so  much  WARMER  than  LIGHT  ONES  ? 

A.  Because  dark  colors  absorb  heat 
from  the  sun  more  abundantly  than  light 
ones. 

Q.      How  can  you  prove  that  DARK  colors  are 

WARMER  than  LIGHT  OWS? 


176  COMMUNICATION    OF    HEAT. 

A.  If  a  piece  of  black  and  a  piece  of 
white  cloth  were  laid  upon  snow,  in  a 
few  hotirs  the  black  cloth  will  have  melted 
the  snow  beneath;  whereas,  the  white 
cloth  will  have  produced  little  or  no  effect 
upon  it  at  all. 

N.  B.  The  darker  any  color  is,  the  warmer  it  is,  be- 
cause it  is  a  better  absorbent  of  heat.  The  order  may  be 
thus  arranged: — 1. — Black  (warmest  of  all). — 2.  Violet. — 
3.  Indigo.— 4.  Blue.— 5.  Green.— 6.  Red.— 7.  Yellow:  and 
8.  White  (coldest  of  all). 

Q.  Why  are  BLACK  KID  GLOVES  unpleasantly 
HOT  for  summer  wear  ? 

A.  1st — Because  black  absorbs  tJie 
sola?'  heat;  and 

2dly — Kid  will  not  allow  the  heat  of 
our  hand  to  escape  through  the  glove. 

Q.  Why  are  LISLE  THREAD  GLOVES  agreeably 
COOL,  for  summer  wear  ? 

A.  1st — Because  thread  absorbs  per- 
spiration :  and 

2dly — It  conducts  away  the  heat  of  our 
hot  hands. 

Q.      Are  Lisle  thread  gloves   ABSORBENTS  of 

heat  ? 

A.  No ;  Lisle  thread  gloves  are  gen- 
erally of  a  grey  or  lilac  color  ;  and,  there- 
fore, do  not  absorb  solar  heat. 

Q.  Why  is  a  PLATE-WARMER  made  of  UN- 
PAINTED  BRIGHT  TIN  ? 

A.     Because  bright  tin  reflects  the  heat 


REFLECTOR — HOAR   FROST.  177 

(which  issues  from  the  fire  in  rays)  upon 
the  meat ;  and,  therefore,  greatly  assists 
the  process  of  roasting-. 

Reflects  the  heat,  i.  e.,  throws  it  back  upon  the  meat. 

Q.  Why  would  not  the  tin  REFLECTOR  do  as 
well,  if  it  were  PAINTED? 

A.  Because  it  would  then  absorb  heat, 
and  not  reflect  it  at  all.  A  plate-warmer 
should  never  be  painted,  but  should  be 
kept  very  clean,  bright,  and  free  from  all 
scratches. 

Q.  Why  should  a  REFLECTOR  be  kept  so  very 
CLEAN  a?id  free  from  all  SCRATCHES? 

A.  Because  if  a  reflector  were  spotted, 
dullj  or  scratched,  it  would  absorb  heat, 
instead  of  reflecting  it ;  and,  consequently, 
would  be  of  no  use  whatsoever  as  a 
reflector. 

Q.  Why  does  HOAR  FROST  remain  on  TOMB- 
STONES long  after  it  has  melted  from  the  GRASS  and 
GRAVEL- WALKS  of  a  church-yard  ? 

A.  Because  tomb-stones  (being*  white] 
will  not  absorb  heat,  like  the  darker  grass 
and  gravel ;  in  consequence  of  which, 
they  remain  too  cold  to  thaw  the  frost 
congealed  upon  their  surface. 

Q.  If  black  absorbs  heat,  why  have  those  who 
live  in  HOT  climates  BLACK  SKINS,  and  not  WHITE 
skins,  which  would  not  absorb  heat  at  all  ? 

A.     Because  black  will  not  blister  from 

8* 


178  COMMUNICATION    OP    HEAT. 

the  heat  of  the  sun.  Although,  therefore, 
the  black  skin  of  the  negro  absorbs  heat 
more  plentifully  than  the  white  skin  of  a 
European;  yet  the  blackness  prevents  the 
sun  from  blistering  or  scorching  it. 

Q.  How  is  it  known  that  the,  BLACK  color  pre- 
vents the  sun  from  either  BLISTERING  or  SCORCHING 
the  skin? 

A.  If  you  put  a  white  glove  on  one 
hand,  and  a  black  glove  on  the  other 
(when  the  sun  is  burning*  hot),  the  hand 
with  the  white  glove  will  be  scorched,  but 
not  the  other. 

Q.       WHICH  hand  will  FEEL  the  HOTTER  ? 

A.  The  hand  with  the  black  glove 
w'Mfeel  the  hotter,  but  will  not  be  scorch- 
ed by  the  sun ;  whereas,  the  hand  with 
the  white  glove  (though  much  cooler)  will 
be  severely  scorched. 

Q.  Why  does  the  BLACK  skin  of  a  NEGRO  NE- 
VER SCORCH  or  BLISTER  with  the  hot  sun  ? 

A.  Because  the  black  color  absorbs 
the  heat — conveys  it  below  the  surface  of 
the  skin — and  converts  it  to  semible  heat 
and  perspiration. 

Q.  Why  does  the  WHITE  EUROPEAN  SKIN 
BLISTER  and  SCORCH  when  exposed  to  the  hot  sun? 

A.  Because  white  will  not  absorb  heat ; 
and,  therefore,  the  hot  sun  rests  on  the 
surface  of  the  skin,  and  scorches  it. 


REFLECTION    OF    HEAT. 


179 


Q.       Why  has  a  NEGRO  BLACK  EYES  ? 

A.  Because  the  black  color  defends 
them  from  the  strong*  light  of  the  tropi- 
cal sun.  If  a  negro's  eyes  were  not 
black,  the  sun  would  scorch  them,,  and 
every  negro  would  be  blind. 

Q.  Why  is  WATER  (in  hot  weather)  KEPT 
COOLER  in  a  BRIGHT  TIN  POT  than  in  an  EARTHEN 
one  ? 

A.  Because  bright  metal  will  not 
absorb  heat  from  the  hot  air,  like  an 
earthen  vessel ;  in  consequence  of  which, 
the  water  is  kept  cooler. 

Boiling  water  is  also  kept  hot  in  bright  metal  better 
than  in  earthen  vessels.  See  p.  187. 


CHAPTER  XVII. 
3. — REFLECTION  OF  HEAT. 

Q.       What  is  meant  by  REFLECTING  HEAT  ? 

A.  To  reflect  heat  is  to  throw  it  back 
in  rays  from  the  surface  of  the  reflecting 
body  towards  the  place  whence  it  came. 

Q.       What  are  the  BEST  REFLECTORS  of  heat  ? 

A.  All  bright  surfaces  and  light  co- 
lors. 

Q.  Are  GOOD  ABSORBERS  of  heat  GOOD  RE- 
FLECTORS also  ? 


180  COMMUNICATION    OF    HEAT. 

A.  No;  those  thing's  which  absorb 
heat  best,  reflect  heat  worst;  and  those 
which  reflect  heat  worst,  absorb  it  best. 

Q.  Why  are  those  things  which  ABSORB  HEAT 
unable  to  REFLECT  it  ? 

A.  Because  if  anything*  sucks  in  heat 
like  a  spong-e,  it  cannot  throw  it  off  from 
its  surface ;  and  if  anything1  throws  off 
heat  from  its  surface,  it  cannot  drink  it  in. 

Q.  Why  are  REFLECTORS  always  made  of 
LIGHT  COLORED  and  highly  POLISHED  METAL  ? 

A.  Because  light  colored  and  highly 
polished  metal  makes  the  best  of  all  re- 
flectors. 

'  Q.       Why  do  not  PLATE-WARMERS  BLISTER  and 
scorch  the  WOOD  behind  ? 

A.  Because  the  brig-lit  tin  front 
throws  the  heat  of  the  fire  back  again, 
and  will  not  allow  it  to  penetrate  to  the 
wood  behind. 

Q.  If  metal  be  such  an  excellent  CONDUCTOR  of 
heat,  how  can  it  REFLECT  heat,  or  throw  it  off? 

A.  Polished  metal  is  a  conductor  of 
heatj  only  when  that  heat  is  communi- 
cated by  actual  contact :  But  whenever 
heat  falls  upon  bright  metal  in  rays^  it  is 
reflected  back  again,  and  the  metal  re- 
mains cool. 

Q.  What  is  meant  "  by  heat  falling  wpon  meted 
IN  RAYS,"  and  not  "  by  contact  ?" 


TIN    REFLECTORS.  181 

A.  If  a  piece  of  metal  were  thrust 
into  a  fire,  it  would  be  in  actual  contact 
with  the  fire ;  but  if  it  were  held  before  a 
fire,  the  heat  of  the  fire  would  fall  upon 
it  in  rays. 

Q.  What  is  the  use  of  the  TIN  SCREEN  or  RE- 
FLECTOR used  in  ROASTING  ? 

A.  It  throws  the  heat  of  the  fire  back 
upon  the  mmt ;  and,  therefore,  both  as- 
sists the  process  of  roasting,  and  helps  to 
keep  the  kitchen  cool. 

Q.      How  does  a  tin  REFLECTOR  tend  to  keep  the 

KITCHEN  COOL  ? 

A.  By  confining  the  heat  of  the  fire  to 
the  hearth,  and  preventing  its  dispersion 
throughout  the  kitchen. 

Q.       Why  are  SHOES  HOTTER  for  being  DUSTY  ? 

A.  Because  dull,  dusty  shoes  will 
absorb  heat  from  the  sun,  earth,  and  air ; 
but  shoes  brightly  polished  throw  off 
the  heat  of  the  sun  by  reflection. 

Q.       Why  does  it  always  FREEZE  on  the  TOP  of 

0,  MOUNTAIN? 

A.  1st — Because  the  air  on  a  moun- 
tain is  very  rarefied ;  and  rarefied  air  re- 
tains more  heat  in  the  latent  form  than 
denser  air  does :  and 

2dly — Air  is  heated  by  the  reflection  of 
the  earth,  and  not  by  solar  rays ;  therefore 
a  mountain-top  (which  is  deprived  of  this 
reflection)  remains  intensely  cold. 


182  COMMUNICATION    OF    HEAT. 

CHAPTER  XVIII. 

4. — RADIATION. 
Q.       What  is  meant  by  RADIATION  ? 

A.  Radiation  means  the  emission  of 
rays:  thus  the  sun  radiates  both  light 
arid  heat ;  that  is,  it  emits  rays  of  liglti 
and  heat  in  all  directions. 

Q.  WHEN  is  heat  RADIATED  from  one  body  to 
another  ? 

A.  When  the  two  bodies  are  separated 
by  a  non-conducting  medium  :  thus  the 
sun  radiates  heat  towards  the  earth,  be- 
cause the  air  (which  is  a  very  bad  con- 
ductor) comes  between. 

Q.       On  WHAT  does  RADIATION  DEPEND  ? 

A.  On  the  roughness  of  the  radiating 
surface :  thus,  if  metal  be  scratched,  its 
radiating-  power  is  increased ;  because 
the  heal;  has  more  points  to  escape  from. 

Q.       Does  a  FIRE  RADIATE  heat  ? 

A.  Yes ;  and  because  burning  fuel 
emits  rays  of  heat,  therefore  we  feel  warm 
when  we  stand  before  a  fire. 

Q.  Why  does  our  FACE  FEEL  uncomfortably 
HOT  when  ice  approach  a  FIRE  ? 

A.  Because  the  fire  radiates  heat 
upon  the  face ;  which  (not  being  covered) 
feels  the  effect  immediately. 


RADIATION — BLACK    LEAD.  183 

Q.  Why  does  the  fire  catch  the  FACE  more  than 
it  does  the  REST  of  the  body  ? 

A.  Because  the  rest  of  the  body  is 
covered  with  clothing1 ;  which  (being*  a 
bad  conductor  of  heat)  prevents  the  same 
sudden  and  rapid  transmission  of  heat  to 
the  skin. 

Q.  Do  those  substances  which  RADIATE  heat 
ABSORB  heat  also  ? 

A.  Yes.  Those  substances  which 
radiate  most,  also  absorb  most  heat;  and 
those  which  radiate  least,  also  absorb  the 
least  heat. 

Q.       Does  anything  ELSE  radiate  heat  BESIDES 

the  SUN  and  FIRE  ? 

A.  Yes :  all  thing's  radiate  heat  in 
some  measure,  but  not  equally  well. 

Q.      WHAT  things  RADIATE  'heat  the  NEXT  BEST 

to  the  sun  and  fire  ? 

A.  All  dull  and  dark  substances  are 
good  radiators  of  heat ;  but  all  light  and 
polished  substances  are  bad  radiators. 

Q.  Why  should  the  FLUES  (connected  with 
stoves,  4*c.,)  be  always  BLACKENED  with  BLACK  LEAD? 

A.  In  order  that  the  heat  of  the  flue 
may  be  more  readily  diffused  throughout 
the  room.  Black  lead  radiates  heat  more 
freely  than  any  other  known  substance. 

In  heating  a  room  with  steam  it  would  be  ahsurd  to  use 
black  pipes  for  conveying  the  steam,  because  they  would 
tend  to  cool  the  hot  vapor. 


184  COMMUNICATION    OF    HKAT. 

Q.  Why  does  a  POLISHED  METAL  TEA-POT  make 
BETTER  TEA  than  a  black  earthen  one  ? 

A.  Because  polished  metal  (being*  a 
very  bad  radiator  of  heat)  keeps  me  water 
hot  much  longer ;  and  the  hotter  the  wa- 
ter is,  the  better  it  "  draws77  the  tea. 

Q.  Why  will  not  a  DULL  BLACK  TEA-POT  make 
good  tea  ? 

A.  .Because  the  heat  of  the  water 
flies  off  so  quickly  through  the  dull  black 
surface  of  the  tea-pot,  that  the  water  is 
very  rapidly  cooled,  and  cannot  "  draw  " 
the  tea. 

Q.  Do  not  pensioners  and  aged  cottagers  gene- 
rally prefer  the  little  BLACK  EARTHEN  TEA-POT  to  the 
bright  METAL  one  ? 

A.  Yes ;  because  they  set  it  on  the 
hob  "to draw;"  in  which  case,  the  little 
black  tea-pot  will  make  the  best  tea. 

Q.  Why  will  a  BLACK  TEA-POT  make  better  tea 
than  a  bright  metal  one,  if  it  be  set  upon  the  HOB  to 
DRAW? 

A.  Because  the  black  tea-pot  will 
absorb  heat  plentifully  from  the  fire,  and 
keep  the  water  hot:  whereas,  a  bright 
metal  tea-pot  (set  upon  the  hob)  would 
throw  off  the  heat  by  reflection. 

Q.  Then  sometimes  a  BLACK  EARTHEN  tea-pot 
is  the  best,  and  sometimes  a  bright  metal  one  ? 

A.     Yes ;  when  a  tea-pot  is  set  on  the 


SAUCEPAN — KETTLE.  185 

hob  "to  draw"  black  earth  is  the  best} 
because  it  absorbs  heat  :  But,  when  a 
tea-pot  is  not  set  on  the  hob,  bright  met- 
al is  the  best ;  because  it  radiates  heat 
very  slowly,  and  therefore  keej}s  the  water 
hot. 

Q.  Why  does  a  SAUCEPAN  which  has  been  USED 
boil  in  a  shorter  time  than  a  NEW  ONE  ? 

A.  Because  the  bottom  and  back  are 
covej^ed  with  soot ;  and  black  soot  rapidly 
absorbs  tlie  heat  of  the  glowing1  coals. 

Q.  Why  should  the  FRONT  and  LID  of  a  SAUCE- 
PAN be  dean  and  BRIGHT? 

A.  Because  they  cannot  absorb  heat, 
as  they  do  not  come  in  contact  with  the 
fire ;  and  (being  bright)  they  will  not 
suffer  the  heat  to  escape  by  radiation. 

Q.  In  what  state  should  a  SAUCEPAN  be  in  or- 
der that  it  may  BOIL  QUICKLY  ? 

A.  All  those  parts  which  come  in 
contact  with  the  fire,  should  be  covered 
with  soot,  in  order  to  absorb  heat ;  but 
all  the  rest  of  the  saucepan  should  be  as 
bright  as  possible,  to  prevent  the  escape 
of  heat  by  radiation. 

Q.  Why  should  NOT  the  BOTTOM  and  BACK  of 
a  kettle  be  CLEANED  and  polished  ? 

A.  Because,  they  come  in  contact  with 
the  fire,  and  (while  they  are  covered  with 


186  COMMUNICATION    OP    HEAT. 

black  soot)  absorb  heat  freely  from  the 
burning*  coals. 

Q.  Why  should  the  FRONT  and  TOP  of  a  kettle 
be  CLEAN  and  well  polished  ? 

A.  Because  polished  metal  will  not 
radiate  heat;  and,  therefore,  (while  the 
front  and  top  of  the  kettle  are  well  pol- 
ished) the  heat  is  kept  in,  and  not  suffered 
to  escape  by  radiation. 

Q.  Why  is  the  BOTTOM  of  a  KETTLE  nearly 
COLD  when  the  WATER  is  BOILING  HOT  ? 

A.  Because  black  soot  is  a  very  bad 
conductor  of  heat ;  and,  therefore,  the  heat 
of  the  boiling-  water  is  some  time  before 
it  gets  through  the  soot  which  adheres  to 
the  bottom  of  the  kettle. 

Q.       Why  is  the  LID  of  a  KETTLE  intensely  HOT  • 
when  the  water  boils  ? 

A.  Because  the  br%ht  metal  lid  is  an 
admirable  conductor  ;  and,  therefore,  the 
heat  from  the  boiling  water  pours  into  our 
hand  the  moment  we  touch  it. 

Q.       Show  the  benefit  of  SMOKE  in  COOKING  ? 

A.  The  carbon  of  the  fuel  (which 
flies  off  in  smoke)  naturally  blackens  all 
culinary  vessels  set  upon  the  fire  to  boil, 
and  thus  renders  them  fit  for  use. 

"Culinary  vessels"  are  vessels  used  in  kitchens  for 
cooking,  as  saucepans,  boilers,  kettles,  &c.,  (from  the  Latin 
word  "  Culina,"  a  kitchen.) 


SMOKE — BRIGHT    METAL;  187 

Q.  How  does  SMOKE  make  culinary  vessels  FIT 
for  USE  ? 

A.  By  absorbing-  heat.  If  it  were 
not  for  the  smoke  (which  gathers  round 
a  kettle  or  saucepan)  heat  would  not  be 
absorbed,  and  the  process  of  boiling  would 
be  greatly  retarded. 

Q.  Why  is  boiling  water  KEPT  HOT  in  a 
BRIGHT  METAL  pot  better  than  in  an  earthen  vessel  ? 

A.  Because  bright  metal  (being  a 
bad  radiator}  will  not  throw  off  from  its 
surface  the  heat  of  the  boiling  water. 

Q.  Would  a  metal  pot  serve  to  keep  water  hot 
if  it  were  DULL  and  DIRTY  ? 

A.  No.  It  is  the  bright  polish  of  the 
metal  which  makes  it  a  bad  radiator :  if 
it  were  dull,  scratched,  or  dirty,  the  heat 
would  escape  very  rapidly. 

Water  in  hot  weather  is  also  kept  cooler  in  bright  metal 
than  in  dull  or  earthen  vessels.     See  p.  179. 

Q.  Why  are  DINNER-COVERS  made  of  BRIGHT 
TIN  or  SILVER  1 

A.  Because  light-colored  and  highly- 
polished  metal  is  a  very  bad  radiator  of 
heat ;  and,  therefore,  bright  tin  or  silver 
will  not  allow  the  heat  of  the  cooked  food 
to  escape  through  the  cover  by  radiation. 

Q.  Why  should  a  MEAT-COVER  be  very  brightly 
POLISHED  ? 

A.     To  prevent  the  heat  of  the  food 


188  COMMUNICATION    OP    HEAT. 

from  escaping-  by  radiation.  If  a  meat- 
cover  be  dull  or  scratched,  it  will  absorb 
heat  from  the  food  beneath ;  and  (instead 
of  keeping-  it  hot)  make  it  cold. 

Q.  Why  should  a  SILVER  MEAT-COVER  be 
PLAIN  and  not  CHASED  ? 

A.  Because  a  chased  meat-cover 
would  absorb  heat  from  tlw  food;  and 
(instead  of  keeping  it  hot)  make  it  cold. 

Q.       What  is  DEW? 

A.  Dew  is  the  vapor  of  tJie  air  con- 
densed by  coming-  in  contact  with  bodies 
colder  than  itself. 

Q.  Why  is  the  GROUND  sometimes  COVERED 
with  DEW? 

A.  Because  the  surface  of  the  earth 
(at  sun-set)  is  made  so  very  cold  by  radi- 
ation, that  the  warm  vapor  of  the  air  is 
chilled  by  contact,  and  condensed  into 
dew. 

Q.  Why  is  the  EARTH  made  colder  than  the 
AIR  after  the  sun  has  set  ? 

A.  Because  the  earth  radiates  heat 
very  freely,  but  the  air  does  not ;  in  con- 
sequence of  which,  the  earth  is  often  5 
or  10  degrees  colder  than  the  air  (after 
sun-set)  ;  although  it  was  much  warmer 
than  the  air,  during  the  whole  day. 

Q.  Why  is  the  EARTH  WARMER  than  the  AIR 
during  the  day  ? 


DEW. 


189 


A.  Because  the  earth  absorbs  solar 
heat  very  freely,  but  the  air  does  not ;  in 
consequence  of  which,  it  is  often  many  de- 
grees warmer  than  the  air,  during  the  day. 

Q.  Why  is  the  surface  of  the  GROUND  COLDER 
in  a  FINE  dear  NIGHT  than  in  a  CLOUDY  one  ? 

A.  Because,  on  a  fine,  clear  star-light 
night,  heat  radiates  from  the  earth  freely, 
and  is  lost  in  open  space  :  but  on  a  dull 
night,  the  clouds  arrest  the  process  of  ra- 
diation. 

Q.  Why  is  DEW  deposited  only  on  a  FINE,  ckar 
NIGHT  ? 

A.  Because  the  surface  of  the  ground 
radiates  heat  most  freely  on  a  fine  night ; 
and  (being  cooled  down  by  this  loss  of 
heat)  chills  the  vapor  of  tlie  air  into  dew. 

Q.  Why  is  there  NO  DEW  on  a  dull^  CLOUDY 
NIGHT  ? 

A.  Because  the  clouds  arrest  the 
radiation  of  heat  from  the  earth  ;  and  (as 
the  heat  cannot  freely  escape)  the  sur- 
face is  not  sufficiently  cooled  down  to 
chill  the  vapor  of  the  air  into  dew. 

Q.  Why  is  a  CLOUDY  NIGHT  WARMER  than  a 
FINE  one  ? 

A.  Because  the  clouds  prevent  the 
radiation  of  heat  from  the  earth  ;  in  con- 
sequence of  which,  the  surface  of  the 
earth  remains  warmer. 


190  COMMUNICATION    OF    HEAT. 

Q.  Why  is  DEW  most  ABUNDANT  in  situations 
most  EXPOSED  ? 

A.  Because  the  radiation  of  heat  is 
not  arrested  by  houses,  trees,  hedges,  or 
any  other  thing*. 

Q.  Why  is  there  scarcely  any  DEW  under  a 
shady  TREE  ? 

A.  1st — Because  the  shady  head  of 
a  tree  arrests  the  radiation  of  heat  from 
the  earth :  and 

2dly — A  leafy  tree  radiates  some  of 
its  own  heat  toicards  the  earth  ;  in  conse- 
quence of  which,  the  ground  underneath 
a  tree  is  not  sufficiently  cooled  down  to 
chill  the  vapor  of  the  air  into  dew. 

Q.  Why  is  there  never  much  DEW  at  the  foot 
of  WALLS  and  HEDGES  ? 

A.  1st — Because  they  act  as  screens, 
to  arrest  the  radiation  of  heat  from  the 
earth:  and 

2dly — They  themselves  radiate  some 
portion  of  heat  towards  the  earth  ;  in 
consequence  of  which,  the  ground  at  the 
foot  of  walls  and  hedges  is  not  sufficiently 
cooled  down,  to  chill  the  vapor  of  the  air 
into  dew. 

Q.  Why  is  there  little  or  NO  DEW  beneath,  a 
FLOWER-AWNING,  although  that  awning  be  open  on 
all  four  sides  ? 

A.     1st — Because  the  awning  arrests 


FROST — SNOW.  191 

the  radiation  of  heat  from  the  ground 
beneath :  and 

2dly — It  radiates  some  of  its  own  heat 
downwards ;  in  consequence  of  which, 
the  ground  beneath  an  awning-  is  not 
sufficiently  cooled  down,  to  chill  the  va- 
por of  air  into  dew. 

Q.  How  can  a  thin  covering  of  BASS  or  even 
MUSLIN  protect  trees  from  FROST  ? 

A.  Because  any  covering  prevents 
the  radiation  of  heat  from  the  tree ;  and 
if  trees  are  not  cooled  down  by  radiation, 
the  vapor  of  the  air  will  not  be  frozen,  as 
it  comes  in  contact  with  them. 

Bass  pronounce  bas — a  kind  of  matting  used  by  garden- 
ers. 

Q.  Why  is  the  BASS  or  CANVASS  itself  (which, 
covers  the  tree)  always  DRENCHED  with  DEW  ? 

A.  Because  it  radiates  heat  both  up- 
wards and  dowmcards ;  in  consequence 
of  which,  it  is  so  cooled  down  that  it  rea- 
dily chills  the  vapor  of  the  air  into  dew. 

Q.  Why  does  SNOW  (at  the  foot  of  a  HEDGE  or 
WALL)  melt  sootier  than  that  in  an  open  field? 

A.  Because  the  hedg*e  or  wall  radi- 
ates heat  into  the  snow  beneath,  which 
melts  it. 

Q.       Why  is  there  NO  DEW  after  a  WINDY  NIGHT  ? 
A.     1st — Because  the  wind  evaporates 


192  COMMUNICATION    OP    HEAT. 

the  moisture,  as  fast  as  it  is  deposited : 
and 

2dly — It  disturbs  the  radiation  of  heat ; 
and  thus  diminishes  the  deposition  of 
dew. 

Q.  Why  are  VALLEYS  and  HOLLOWS  often 
thickly  covered  with  DEW,  although  they  are  sheltered  ? 

A.  Because  the  surrounding  hills 
prevent  the  repose  of  air  from  being  dis- 
turbed; but  do  not  overhang  and  screen 
the  valleys  sufficiently  to  arrest  their  ra- 
diation. 

Q.  Why  does  DEW  fall  more  ABUNDANTLY  on 
SOME -THINGS  than  on  OTHERS  ? 

A.  Because  some  things  radiate  heat 
more  freely  than  others  ;  and,  therefore, 
become  much  cooler  in  the  night. 

Q.  Why  are  things  which  RADIATE  HEAT 
MOST  FREELY  always  the  most  THICKLY  COVERED 
with  DEW  ? 

A.  Because  the  vapor  of  the  air  is 
chilled  into  dew,  the  moment  it  comes  in 
contact  with  them. 

Q.      WHAT  kind  of  things  RADIATE  HEAT  most 

FREELY  1 

A.  Grass,  wood,  and  the  leaves  of 
plants,  radiate  heat  very  freely :  but  pol- 
ished metal,  smooth  stones,  and  woollen 
cloth,  part  with  their  heat  very  tardily. 

Q.      Do  the  Leaves  of  ALL  plants  radiate  heat 

EQUALLY  WELL  ? 


VEGETABLES.  193 

A.  No.  Rough,  woolly  leaves  (like 
those  of  a  holly-hock)  radiate  heat  much 
more  freely  than  the  hard,  smooth,  polished 
leaves  of  a  common  laurel. 

Q.  Show  the  WISDOM  of  GOD  in  making  grass, 
the  leaves  of  trees,  and  ALL  VEGETABLES,  EXCELLENT 
RADIATORS  of  heat  ? 

A.  As  vegetables  require  much  mois- 
ture, and  would  often  perish  without  a 
plentiful  deposit  of  dew,  God  wisely 
made  them  to  radiate  heat  freely,  so  as  to 
chill  the  vapor  (which  touches  them)  in- 
to dew. 

Q.  Will  polished' METAL,  smooth  STONES,  and 
woollen  CLOTH,  readily  collect  DEW  ? 

A.  No.  While  grass  and  the  leaves 
of  plants  are  completely  drenched  with  dew 
a  piece  of  polished  metal,  or  of *  woollen  cloth 
(lying  on  the  same  spot),  will  be  almost 
dry. 

Q.  Why  would  POLISHED  METAL  and  WOOL- 
LEN CLOTH  be  DRY,  while  grass  and  leaves  are 
drenched  with  DEW  ? 

A.  Because  the  polished  metal  and 
woollen  cloth  part  with  their  heat  so  slow- 
ly, that  the  vapor  of  the  air  is  not  chilled 
into  dew  as  it  passes  over  them. 

Q.  Why  is  a,  GRAVEL  WALK  almost  DRY,  when 
a  grass  plat  is  covered  thick  with  DEW  ? 

A.     Because  grass  is  a  good  radiator , 
9 


194  COMMUNICATION    OF    HEAT. 

and  throws  off  its  heat  very  freely ;  but 
gravel  is  a  very  bad  radiator,  and  parts 
with  its  heat  very  slowly. 

Q.  Is  that  the  reason  why  GRASS  is  SATURATED 
\tilh  DEW,  and  the  GRAVEL  is  NOT  1 

A.  Yes.  When  the  vapor  of  warm 
air  comes  in  contact  with  the  cold  grass, 
it  is  instantly  chilled  into  dew ;  but  it  is 
not  so  freely  condensed  as  it  passes  orer 
gravel,  because  gravel  is  not  so  cold  as 
the  grass. 

Q.  Why  does  DEW  rarely  fall  upon  hard 
ROCKS  and  BARREN  lands  ? 

A.  Because  rocks  and  barren  lands 
are  so  compact  and  hard,  that  they  can 
neither  absorb  nor  radiate  much  heat; 
and  (as  their  temperature  varies  but  very 
little)  very  little  dew  distils  upon  them. 

Q.  Why  does  DEW  fall  more  abundantly  on 
CULTIVATED  soils  than  on  BARREN  lands  ? 

A.  Because  cultivated  soils  (being 
loose  and  porous)  very  freely  radiate  by 
night  the  heat  which  they  absorbed  by 
day ;  in  consequence  of  which,  they  are 
much  cooled  down,  and  plentifully  con- 
dense the  vapor  of  the  passing  air  into 
dew. 

Q.  Show  the  WISDOM  of  GOD  in  this  arrange- 
ment. 

A.     Every  plant   and  inch  of  land, 


GIDEON'S  MIRACLE.  195 

which  needs  the  moisture  of  dew,  is 
adapted  to  collect  it ;  but  not  a  single 
drop  is  wasted  where  its  refreshing*  mois- 
ture is  not  required. 

Q.       Show  the  advantage  to  us  in  having  pol- 
ished METAL  and  woollen  CLOTH  BAD  RADIATORS  of 


A.  If  polished  metal  collected  dew  as 
easily  as  grass,  it  could  never  be  kept  dry 
and  free  from  rust.  Again,  if  woollen 
garments  collected  dew  as  readily  as  the 
leaves  of  trees,  we  should  be  often  soak- 
ing wet.  and  subject  to  constant  colds. 

Q.  Show  how  this  affords  a  beautiful  illustra- 
tion of  GIDEON'S  MIRACLE,  recorded  in  the  book  of 
Judges,  vi.  37,  38. 

A.  The  fleece  of  wool  (which  is  a  very 
bad  radiator  of  heat)  was  soaking-  wet 
with  dew,  when  the  grass  (which  is  a 
most  excellent  radiator)  was  quite  dry. 

Q.  Was  not  this  CONTRARY  to  the  laws  of 
NATURE  ? 

,  A.  Yes ;  and  was,  therefore,  a  plain 
demonstration  of  the  power  of  God,  who 
could  thus  change  the  very  nature  of 
things  at  his  will. 

Q.  Why  do  our  CLOTHES  FEEL  DAMP,  after 
walking  in  a  fine  evening  in  SPRING  or  AUTUMN  ? 

A.  Because  the  vapor  (condensed  by 
the  cold  earth)  lights  upon  them  like  dew. 


196  COMMUNICATION    OF    HEAT. 

Q.  Why  are  WINDOWS  often  covered  with  thick 
MIST,  and  the  frames  wet  with  standing  WATER? 

A.  Because  the  temperature  of  the 
external  air  always  falls  at  sunset,  and 
chills  the  window-glass  with  which  it 
comes  in  contact. 

Q.  How  does  this  account  for  the  MIST  and  WA- 
TER on  a  WINDOW  ? 

A.  As  the  warm  vapor  of  the  room 
touches  the  cold  glass  it  is  chilled  and  con- 
densed into  mist ;  and  the  mist  (collect- 
ing* into  drops)  rolls  down  the  window- 
frame  in  little  streams  of  water. 

Q.  Does  'the  GLASS  of  a  window  COOL  down 
more  RAPIDLY  than  the  AIR  of  the  room  itself? 

A.  Yes;  because  the  air  is  kept 
warm  by  fires,  and  by  the  animal  heat 
of  the  people  in  the  room ;  in  consequence 
of  which,  the  air  of  a  room  suffers  vzry 
little  diminution  of  heat  from  the  setting 
of  the  sun. 

Q.       Whence  arises  the  VAPOR  of  a  ROOM  ? 

A.  1st — The  very  air  of  the  room 
contains  vapor  : 

2dly — The  breath  and  insensible  per- 
spiration of  the  inmates  increase  this 
vapor:  and 

3dly — ffot  dinners,  the  steam  of  tea} 
and  so  on?  increase  it  still  more. 


MIST — VAPOR.  197 

Q.  What  is  meant  by  "  the  INSENSIBLE  PER- 
SPIRATION?" , 

A.  From  every  part  of  the  human 
body,  an  insensible  and  invisible  perspi- 
ration issues  all  night  and  day ;  not  only 
in  the  hot  weather  of  summer,  but  also 
in  the  coldest  day  of  winter. 

Q.  If  the  perspiration  be  both  INSENSIBLE  and 
INVISIBLE,  how  is  it  KNOWN  that  there  is  any  such 
perspiration  ? 

A.  If  you  put  your  naked  arm  into  a 
clean,  dry  glass  tube,  the  perspiration  will 
condense  on  the  glass  like  mist. 

Q.  Why  are  CARRIAGE  WINDOWS  very  SOON 
covered  with  thick  MIST  ? 

A.  Because  the  warm  vapor  of  the 
carriage  is  condensed  by  the  cold  glass, 
and  covers  it  with  a  thick  mist. 

Q.  WHY  is  the  glass  window  COLD  enough  to 
condense  the  vapor  of  the  carriage  ? 

A.  Because  the  inside  of  a  carriage 
is  much  warmer  than  the  outside  ;  and 
the  glass  window  is  made  cold  by  con- 
tact with  the  external  air. 

Q.  WHERE  does  the  WARM  vapor  of  the  car- 
riage come  from  ? 

A.  The  warm  breath  and  insensible 
perspiration  of  the  persons  riding,  load 
the  air  of  the  carriage  with  warm  vapor. 

Q.  What  is  the  cause  of  the  pretty  FROST- 
WORK, seen  on  bed-room  WINDOWS  in  winter-time  ? 


198  COMMUNICATION    OF    HEAT. 

A.  The  breath  and  insensible  perspi- 
ration of  the  sleeper  (coming*  in  contact 
with  the  ice-cold  window)  are  frozen  by 
the  cold  glass,  arid  form  those  beautiful 
appearances  seen  in  our  bed-rooms  on  a 
winter  morning. 

Q.  Why  is  the  GLASS  of  a  window  colder  than 
the  WALLS  of  a  room  ? 

A.     Because  glass  is  so  excellent  a  ra 
diator,  that  it  parts   with  its  heat  more 
rapidly  than  the  walls  do. 

Q.  Why  is  a  TUMBLER  of  cold  WATER  made 
quite  DULL  with  mist,  when  brought  into  a  room 

FULL  of  PEOPLE  ? 

A.  Because  the  hot  vapor  of  the  room 
is  condensed  upon  the  cold  tumbler,  with 
which  it  comes  in  contact ;  and  changes 
its  invisible  and  gaseous  form  into  that 
of  a  thick  mist. 

Q.  Why  is  a  GLASS  made  quite  DULL  by  lay- 
ing a  HOT  HAND  upon  it  ? 

A.  Because  the  insensible  perspiration 
of  the  hot  hand  is  condensed  upon  the  cold 
glass,  and  made  perceptible. 

Q.  WJiy  are  WINE-GLASSES  made  quite  DULL, 
when  they  are  brought  into  a  room  FULL  O/*COMPANY? 

A.  Because  the  hot  vapor  of  the 
room  (coming  in  contact  with  the  cold 
wine-glasses)  is  condensed  upon  them,, 
and  covers  them  with  vapor,  like  dew. 


WINE    GLASS — WALLS.  199 

Q.  Why  does  this  misty  appearance  GO  OFF, 
after  a  little  time  ? 

A.  Because  the  glass  becomes  of  the 
same  temperature  as  the  air  of  the  room ; 
and  will  no  longer  chill  the  vapor  which 
touches  it,  and  condense  it  into  mist. 

Q.  Why  is  a  WINE  GLASS  (which  has  been 
brought  out  of  a  CELLAR  into  the  AIR)  covered  with 
a  thick  MIST  in  summer-time  ? 

A.  Because  the  vapor  of  the  hot  air 
is  condensed  into  a  thick  mist,  by  contact 
with  the  cold  glass. 

Q.  Why  does  BREATHING  on  a  GLASS  make  it 
quite  DULL  ? 

A.  Because  the  hot  breath  is  con- 
densed by  the  cold  glass ;  and  therefore 
covers  it  with  a  thick  mist. 

Q.  Why  are  the  WALLS  of  a  house  covered 
with  WET  in  a  sudden  THAW  ? 

A.  Because  the  walls  (being  thick) 
cannot  change  their  temperature  so  fast 
as  the  air ;  in  consequence  of  which,  they 
retain  their  cold  after  the  thaw  has  set  in. 

Q.  How  does  "  RETAINING  their  COLD"  account 
for  their  being  so  WET  ? 

A.  As  the  vapor  of  the  warm  air 
touches  the  cold  walls,  it  is  chilled  and 
condensed  into  water ;  which  either  sticks 
to  the  walls  or  trickles  down  in  little 
streams. 


200  COMMUNICATION    OF    HEAT. 

Q.  Why  does  a  thick  WELL-BUILT  HOUSE  con- 
tract more  DAMP  of  this  kind  than  an  ORDINARY 
one  ? 

A.  Because  the  walls  are  much 
thicker  ;  and  (if  the  frost  has  penetrated 
far  into  the  bricks]  they  will  be  some 
time  before  they  are  reduced  to  the  same 
temperature  as  the  air. 

Q.  Why  are  BALUSTERS,  <^c.,  DAMP  after  a 
THAW  ? 

A.  Because  they  are  made  of  some 
very  close-grained  varnished  wood, 
which  cannot  change  its  temperature  so 
5  as  the  air. 


Balusters — corruptly  called  banisters. 
Q.       How  does  THIS  account  for  the  BALUSTERS 
being  DAMP  ? 

A.  The  vapor  of  the  warm  air  (com- 
ing1 in  contact  with  the  cold  balusters)  is 
chilled  and  condensed  into  water  upon 
them. 

Q.  Why  is  our  BREATH  VISIBLE  in  WINTER, 
and  NOT  in  SUMMER  ? 

A.  Because  the  intense  cold  con- 
denses our  breath  into  visible  vapor; 
but  in  summer  the  air  is  not  cold  enough 
to  do  so. 

Q.  Why  are  our  HAIR  and  the  BRIM  of  our 
HAT  often  covered  with  little  drops  of  pearly  DEW 
in  winter -time  ? 

A.     Because  our  breath  is  condensed 


WINDS — MOISTNESS.  201 

as  soon  as  it  comes  in  contact  with  our 
cold  hair  or  hat,  and  hangs  there  in  little 
dew-drops. 

Q.  Why  does  the  STEAM  of  a  RAILWAY  BOILER 
often  pour  down,  like  fine  rain,  when  the  steam  is 
« let  of?" 

A.  Because  in  cold  weather  the 
steam  from  the  chimney  is  condensed  by 
the  chill  air  and  falls  like  fine  rain. 

Q.  Why  is  there  LESS  DEW  when  the  WIND  is 
WESTERLY,  than  when  the  wind  is  EASTERLY  ? 

A.  Because  westerly  winds  cross  the 
continent,  and,  (as  they  pass  over  land) 
are  dry  and  arid:  But  easterly  winds 
cross  the  Atlantic  Ocean,  and  (as  they 
pass  over  water]  are  moist  and  fall  of 
vapor. 

Q.      How  does  the  DRYNESS   of  a  westerly  wind 

PREVENT  DEW-FALLS  ? 

A.  As  westerly  winds  are  very  dry, 
they  imbibe  the  moisture  of  the  air ;  in 
consequence  of  which,  there  is  very  little 
left  to  be  condensed  into  dew. 

Q.  How  does  the  MOISTNESS  of  an  eastern  wind 
PROMOTE  dew-falls  ? 

A.  As  easterly- winds  are  saturated 
with  vapor,  they  require  very  little  re- 
duction of  heat  to  cause  a  copious  deposi- 
tion of  dew. 

Q.       When  is  DEW  most  COPIOUSLY  distilled  ? 
9* 


202  COMMUNICATION    OF    HEAT. 

A.  After  a  hot  day  in  summer  or 
autumn,  especially  if  the  wind  be  easterly. 

Q.  Why  is  DEW  distilled  most  COPIOUSLY  af- 
ter- a  HOT  day  ? 

A.  Because  the  surface  of  the  hot 
earth  radiates  heat  very  freely  at  sunset, 
and  (being  made  much  colder  than  the 
air)  cfulls  the  passing  vapor  and  con- 
denses it  into  dew. 

Q.  Does  not  AIR  radiate  heat,  as  well  as  the 
i EARTH  and  its  various  plants  ? 

A.  No.  The  air  never  radiates  heat ; 
nor  is  the  air  made  hot  by  the  rays  of 
the  sun. 

Q.      How  is  the  AIR  made  HOT  or  COLD  ? 

A.  By  convection  of  hot  or  cold  cur- 
rents. 

Q.      Explain  this. 

A.  The  air  which  has  been  heated  by 
the  surface  of  the  earth  ascends,  warm- 
ing- the  air  through  which  it  passes. 
Other  air  (being  warmed  in  a  similar 
way)  also  ascends,  carrying  heat;  and 
this  is  repeated,  till  all  the  air  is  made  hot. 

Q.      How  is  the  AIR  made  COLD  ? 

A.  The  air  resting  on  the  earth  is 
made  cold  by  contact :  this  cold  air  makes 
the  air  above  it  cold;  and  cold  currents 
(or  winds)  shake  the  whole  together,  till 
all  becomes  of  one  temperature. 


MOONLIGHT — HONEY-DEW.  203 

Q.  Why  is  MEAT  very  subject  to  TAINT  on  a 
MOONLIGHT  night  ? 

A.  Because  it  radiates  heat  vsry  freely 
in  a  bright  moonlight  night;  in  conse- 
quence of  which,  it  is  soon  covered  with 
de-Wj  which  produces  rapid  decomposition. 

Q.  How  do  MOONLIGHT  nights  conduce  to  the 
rapid  GROWTH  of  PLANTS  ? 

A.  Radiation  is  carried  on  very 
rapidly  on  bright  moonlight  nights  ;  in 
consequence  of  which,  dew  is  very  plen- 
tifully deposited  on  young  plants,  which 
conduces  much  to  their  growth  and  vi- 
gor. 

Q.       Why  is  evening  DEW  INJURIOUS  to  HEALTH  1 

A.  Because  it  is  always  laden  with 
noxious  exhalations  from  the  earth;  espe- 
cially in  marshy  countries. 

Q.       Is  HONEY-DEW  a  similar  thing  to  DEW  £ 

A.  -  No.  Honey-dew  is  a  sweet  liquid 
shed  by  a  very  small  insect  (called  the 
a'phis)  and  deposited  in  autumn  on  the 
under  surface  of  favorite  leaves. 

Frequently  also  on  Lime  Trees,  in  the  Spring. 

Q.  Does  HONEY-D^W  INJURE  leaves,  or  do  them 
good  ? 

A.  It  injures  them  very  much,  by  fill- 
ing the  pores  with  a  thick,  clammy  liquid ; 
in  consequence  of  which,  the  leaf  can 


204  COMMUNICATION    OF    HEAT. 

neither  transpire  nor  absorb  its  needful 
food. 

Q.  What  EFFECT  has  honey-dew  upon  tht 
APPEARANCE  of  a  leaf? 

A.  After  a  little  time,  the  leaf  (being- 
smothered  and  starved)  begins  to  turn  a 
dingy  yellow. 

Q.      Are  not  ANTS  very  FOND  of  HONEY-DEW? 

A.  Yes ;  and  crawl  up  the  loftiest 
trees  in  order  to  obtain  it. 

Q.       What  is  the  cause  of  MIST  (or  earth-fog)  ? 

A.  If  the  night  has  been  very  calm, 
the  radiation  of  heat  from  the  earth  has 
been  very  abundant ;  in  consequence  of 
which,  the  air  (resting-  on  the  earth)  has 
been  chilled,  and  its  vapor  condensed 
into  a  thick  mist. 

Q.       Why  does  not  the  MIST  become  DEW  ? 

A.  Because  the  chill  of  the  air  is  so 
rapid,  that  vapor  is  condensed  faster 
than  it  can  be  deposited;  and  (covering- 
the  earth  in  a  mist)  prevents  any  further 
radiation  of  heat  from  the  earth. 

Q.  When  the  earth  can  no  longer  RADIATE 
heat  upwards,  does  it  continue  to  CONDENSE  the  vapor 
of  the  air  ?  ^ 

A.  No ;  the  air  (in  contact  with  the 
earth)  becomes  about  equal  in  tempera- 
ture with  the  surface  of  the  earth  itself; 
for  which  reason,  the  mist  is  not  con- 


DEW-DROPS.  205 

densed  into   dew,  but   remains  floating 
above  the  earth  as  a  thick  cloud. 

Q.  This  MIST  seems  to  RISE  HIGHER  and. 
HIGHER,  and  yet  remains  quite  as  dense  below  as  at 
first.  Explain  the  cause  of  this. 

A.  The  air  resting*  on  the  earth  is 
first  chilled,  and  chills  the  air  resting1  on 
it ;  the  air  which  touches  this  new  layer 
of  mist  being*  a/so  condensed,  layer  is 
added  to  layer :  And  thus  the  mist  seems 
to  be  rising,  when  (in  fact)  it  is  only 
deepening' 

Q.  Why  do  MIST  and  DEW  VANISH,  as  the  SUN 
rises  ? 

A.  Because  the  air  becomes  warmer 
at  sun-rise,  and  absorbs  the  vapor. 

Q.       Why  is  a  DEW-DROP  ROUND  ? 

A.  Because  every  part  of  it  is  equally 
balanced;  and,  therefore,  there  is  no 
cause  why  one  part  of  the  drop  should 
be  further  from  the  centre  than  anotJier. 

Q.  Why  is  the  DEW-DROP  (on  a  broad  leaf) 
sometimes  FLATTENED  ? 

A.  Because  two  or  more  drops  of 
dew  roll  together,  and  make  one  large 
spheroid  (or  flattened  drop). 

Q.  Why  will  DEW-DROPS  ROLL  ABOUT  CAB- 
BAGE-PLANTS, POPPIES,  <^c.,  without  wetting  the  sur- 
face ?  « 

A.     Because  the  leaves  of  cabbages 


206  COMMUNICATION    OF    HEAT. 

and  poppies  are  covered  with  a  very  fine 
waxen  powder,  over  which  the  dew-drop 
rolls  without  wetting*  the  surface,  as  a 
drop  of  rain  would  over  dust. 

Q.  Why  does  not  a  drop  of  RAIN  WET  the 
DUST  over  which  it  rolls  ? 

A.  Because  dust  has  no  affinity  for 
water,  and,  therefore,  repels  it. 

Q.  Why  does  not  the  DEW-DROP  WET  the  POW- 
DER of  the  CABBAGE-PLANT? 

A.  Because  the  fine  powder  which 
covers  the  cabbage-leaves  has  no  affinity 
for  water,  and,  therefore,  repels  it. 

Q.  Why  will  DEW-DROPS  ROLL  over  a  ROSE, 
<$fc.,  without  wetting  the  petals  ? 

A.  Because  the  leaves  of  a  rose  con- 
tain an  essential  oil,  which  has  no  affinity 
for  water,  and,  therefore,  repels  it. 

Q.  Why  can  SWANS  and  DUCKS  dive  under 
water  WITHOUT  being  WETTED  ? 

A.  Because  their  feathers  are  cover- 
ed with  an  oily  secretion,  which  has  no 
affinity  for  water,  and,  therefore,  re- 
pels it. 

Q.       What  is  the  cause  of  MIST  ? 

A.  Currents  of  iur  from  the  water 
coming-  in  contact  with  colder  land  cur- 
rents. 

Q.  Why  are  the  currents  of  air  from  the  LAND 
COLDER  than  those  blowing  over  WATER,  1 


AIR    AND    WATER.  207 

A.  Because  the  earth  radiates  heat 
after  sun-set  more  freely  than  water; 
consequently  the  air  which  comes  in  con- 
tact with  the  land  is  more  cold  than 
that  which  comes  in  contact  with  water. 

For  other  questions  respecting  land  and  sea  breezes  see~ 
Chapter  XXIV. 

Q.  Why  is  not  the  AIR  which  passes  over 
WATER  so  COOL  as  that  which  passes  over  LAND  ? 

A.  Because  water  does  not  cool 
down  at  sun-set  so  fast  as  land  does  ; 
and,  therefore,  the  air  in  contact  with  it 
remains  warmer. 

Q.  Why  does  not  WATER  cool  down  so  fast  as 
LAND  ? 

A.  1st— Because  the  surface  of  water 
is  perpetually  changing  ;  and,  as  fast  as 
one  surface  is  made  cold,  another  is  pre- 
sented :  and 

2dly — The  moment  water  is  made 
cold  it  sinks,  and  warmer  portions  of  wa- 
ter rise  to  occupy  its  place  :  therefore, 
before  the  surface  of  water  is  cooled,  the 
whole  volume  must  be  made  cold :  which 
is  not  the  case  with  land. 

Q.  What  is  the  +use  of  a  "pea-soup"  LON- 
DON FOG? 

A.  These  fogs  (which  occur  general- 
ly in  the  winter  time)  are  occasioned 
thus  : — Some  current  of  air  (being  sud- 


208  COMMUNICATION    OP    HEAT. 

denly  cooled)  descends  into  the  warm 
streets,  forcing-  back  the  smoke  in  a  mass 
towards  the  earth. 

Q.       Why  are  there  not  FOGS  EVERY  night  ? 

A.  Because  the  air  will  always  hold 
in  solution  a  certain  quantity  of  vapor, 
(which  varies  according1  to  its  tempera- 
ture :)  and,  when  the  air  is  not  saturated, 
it  may  be  cooled  without  parting-  with 
its  vapor. 

Q.       When  do  FOGS  occur  at  night  ? 

A.  When  the  air  is  saturated  with 
vapor  during1  the  day.  When  this  is  the 
case,  it  deposits  some  of  its  superabun- 
dant moisture  in  the  form  of  dew  or  fog* 
as  soon  as  its  capacity  for  holding*  vapor 
is  lessened  by  the  cold  night. 

Q.  Why  is  there  very  OFTEN  a  fog  over 
MARSHES  and  RIVERS,  at  night-time? 

A.  Because  the  air  of  marshes  is 
almost  always  near  saturation;  and, 
therefore,  the  least  depression  of  tempe- 
rature will  compel  it  to  relinquish  some 
of  its  moisture  in  the  form  of  dew  or 


Q.  What  is  the  DIFFERENCE  between  DEW  and 
RAIN? 

A.  In  dew,  the  condensation  is  made 
near  the  earth's  surface. 


MIST   AND   FOG.  209 

In  rain,  the  drops  fall  from  a  consi- 
derable height. 

Q.       What  is  the  CAUSE  of  both  dew  and  rain  ? 

A.  Cold  condensing  the  vapor  of  the 
air  when  near  the  point  of  saturation. 

Q.       Why  do  MIST  and  FOG  VANISH  at  sun-rise? 

A.  Because  the  condensed  particles 
are  again  changed  into  invisible  vapor  by 
the  heat  of  the  sun. 

Q.  What  is  the  difference  between  a  MIST  and  a 
FOG? 

A.  MIST  is  generally  applied  to  va- 
pors condensed  on  marshes,  rivers,  and 
lakes. 

FOG  is  generally  applied  to  vapors 
condensed  on  land;  especially  if  those 
vapors  are  laden  with  smoke. 

Q.  What  is  the  reason  why  condensed  vapor 
sometimes  forms  into  CLOUDS,  and  sometimes  into 
FOG? 

A.  If  the  surface  of  the  EARTH  is 
hotter  than  the  air,  the  vapor  of  the 
earth  is  chilled  by  the  cold  air,  and  be- 
comes FOG:  But  if  the  AIR  is  hotter  than 
the  earth,  the  vapor  rises  through  the  air, 
and  becomes  cLout). 

Q.  If  cold  air  produces  FOG,  why  is  it  not 
foggy  on  a  FR.OSTY  MORNING  ? 

A.  1st — Because  less  vapor  is  formed 
on  a  frosty  day :  and 


210  COMMUNICATION    OF    HEAT. 

2dly — The  vapor  is  frozen  upon  the 
ground,  before  it  can  rise  from  the  earth, 
and  becomes  HOAR-FROST. 

Q.  Why  are  FOGS  more  general  in  AUTUMN 
than  in  spring  ? 

A.  1st — Because  the  air  in  spring  is 
generally  much  drier  than  it  is  in  autumn ; 
in  consequence  of  which,  it  is  not  so  near 
the  point  of  saturation:  and 

2dly — The  earth  in  spring-  is  not  so 
hot  as  it  is  in  autumn ;  in  consequence 
of  which,  its  vapor  is  not  chilled  into  fog 
as  it  issues  into  the  air. 

Q.  Why  are  FOGS  more  common  in  VALLEYS 
than  on  HILLS  ? 

A.  1st  —  Because  valleys  contain 
more  moisture  than  hills  :  and 

2dly — They  are  not  exposed  to  suffi- 
cient wind  to  dissipate  the  vapor. 

Q.      How  does  WIND  dissipate  FOGS  ? 

A.  Either  by  blowing  them  away ; 
or  else  by  dissolving  them  into  vapor 
again. 

Q.       What  is  HOAR-FROST  ? 

A.  Th^re  are  two  sorts  o'  hoar-frost ; 
1 . — FROZEN-  DEW  :  and  2. — I  JOZEN  FOG. 

Q.  What  is  the  cause  of  the  GROUND  HOAR- 
FROST, or  frozen  DEW? 

A.  Very  rapid  radiation  of  heat  from 
the  earth ;  in  consequence  of  which,  the 


HOAR-FROST.  211 

surface  is  so  cooled  down  that  it  freezes 
the  dew  condensed  upon  it. 

Q.       Why  is  HOAR-FROST  seen  only  after  a  very 

CLEAR  NIGHT  ? 

A.  Because  the  earth  will  not  have 
thrown  off  heat  enough  by  radiation  to 
freeze  the  vapor  condensed  upon  its  sur- 
face, unless  the  night  has  been  very  clear 
indeed. 

Q.  Why  does  HOAR-FROST  very  often  COVER 
the  GROUND  and  TREES,  when  the  water  of  rivers  is 
not  frozen  ? 

A.  Because  it  is  not  the  effect  of  cold 
in  the  air,  but  cold  on  the  surface  of  the 
earth  (produced  by  excessive  radiation), 
which  freezes  the  dew  condensed  upon  it. 

Q.  Why  is  the  HOAR-FROST  upon  GRASS  and 
VEGETABLES  much  thicker  than  that  upon  lofty 

TREES  1 

A.  Because  the  air  (resting*  on  the 
surface  of  the  ground)  is  much  colder 
after  sun-set  than  the  air  higher  up ;  in 
consequence  of  which,  more  vapor  is 
condensed  and  frozen  there. 

Q.  Why  is  the  AIR  (resting  on  the  surface  of 
the  EARTH)  colder  than  that  in  the  HIGHER  regions  ? 

A.  Because  the  earth  radiates  more 
heat  than  the  leaves  of  lofty  trees  ;  and, 
therefore,  more  rapidly  condenses  and 
freezes  the  vapor  of  the  air. 


212  COMMUNICATION    OF    HEAT. 

Q.  Why  are  EVERGREENS  often  FROST-BITTED 
when  lofty  trees  are  NOT? 

A.  Because  they  do  not  rise  far  above 
the  surface  of  the  earth ;  and  (as  the  air 
contiguous  to  the  earth  is  made  colder  by 
radiation  than  that  in  the  higher  regions), 
therefore,  the  low  evergreen  is  often  frost- 
bitten,  when  the  lofty  tree  is  uninjured. 

Q.  Why  is  there  little  or  NO  HOAR-FROST  un- 
der SHRUBS  and  shady  TREES  ? 

A.  1st — Because  the  leafy  top  arrests 
the  process  of  radiation  from  the  earth : 

2dly — Shrubs  and  trees  radiate  heat 
towards  the  earth:  and,  therefore,  the 
ground  beneath  is  never  cold  enough  to 
congeal  the  little  dew  which  rests  upon  it. 

Q.  What  is  the  cause  of  that  HOAR-FROST 
which  arises  from  FROZEN  FOG? 

A.  The  thick  fog-  which  invested  the 
earth  during  the  night  (being  condensed 
by  the  cold  frost  of  early  morning),  is  con- 
gealed upon  every  object  with  which  it 
comes  in  contact. 


CONVECTION.  213 

CHAPTER  XIX. 

5. — CONVECTION. 

Q.  What  is  meant  by  the  CONVECTION  of 
HEAT? 

A.  Heat  communicated  by  being 
carried  to  another  thing"  or  place  ;  as  the 
hot  water  resting  on  the  bottom  of  a  ket- 
tle carries  heat  to  the  water  through 
which  it  ascends.  (See  p.  226.) 

Q.       Are  LIQUIDS  good  CONDUCTORS  of  heat  ? 

A.  No ;  liquids  are  bad  conductors  ; 
and  are,  therefore,  made  hot  by  convec- 
tion. 

Q.  Why  are  LIQUIDS  BAD  CONDUCTORS  of 
heat  ? 

A.  Because  heat  converts  a  liquid  into 
steam ;  and  flies  off  with  the  vapor  in- 
stead of  being  conducted  through  the 
liquid. 

Q.       Explain  how  WATER  is  made  HOT. 

A.  The  water  nearest  the  fire  is  jirs* 
heated,  and  (being  heated)  rises  to  the 
top ;  while  its  place  is  supplied  by  colder 
portions,  which  are  'heated  in  turn,  till 
all  the  water  is  boiling  hot. 

Q.  Why  is  WATER  in  such  continual  FERMENT, 
when  it  is  BOILING  1 

A.     This  commotion  is  mainly  produ- 


214  COMMUNICATION    OP    HEAT. 

ced  by  the  ascending  and  descending  cur- 
rents of  hot  and  cold  water. 

The  escape  of  steam  from  the  water  contributes  also  to 
increase  this  agitation. 

Q.       How  do  these  two  currents  PASS  each  other  ? 

A.  The  hot  ascending  current  rises  up 
through  the  centre  of  the  mass  of  water; 
while  the  cold  descending  currents  pass 
down  by  the  metal  sides  of  the  kettle. 

For  other  questions  on  the  subject  of  boiling  water, 
see  from  page  109  to  115. 

Q.  Why  is  HEAT  applied  to  the  BOTTOM,  and 
not  to  the  top  of  a  KETTLE  ? 

A.  Because  the  heated  water  always 
ascends  to  the  surface,  heating1  the  water 
through  which  it  passes ;  if,  therefore, 
heat  were  applied  to  the  top  of  a  vessel, 
the  water  below  the  surface  would  never 
be  heated. 

Q.  As  the  lower  part  of  a  GRATE  is  made  RED- 
HOT  by  the  fire  ABOVE,  why  would  not  the  WATER 
boil,  if  fire  were  applied  to  the  TOP  of  a  kettle  ? 

A.  Tiie  iron  of  a  grate  is  an  excellent 
conductor ;  if,  therefore,  one  part  be  heat- 
ed, the  heat  is  conducted  to  every  other 
part :  But  water  is  a  very  bad  conductor, 
and  will  not  diffuse  heat  in  a  similar  way. 

Q.  Prove  that  WATER  is  a  BAD  CONDUCTOR  of 
heat. 

A.  When  a  blacksmith  immerses  his 
red-hot  iron  in  a  tank  of  water,  the  water 


BOILING    WATER — SOUP.  215 

which  surrounds  the  iron  is  made  boiling 
hot,  while  that  below  the  surface  remains 
quite  cold. 

Q.  If  you  wish  to  COOL  LIQUIDS,  where  should 
the  cold  be  applied? 

A.  To  the  top  of  the  liquid;  because 
the  cold  portions  will  always  descend,  and 
allow  the  warmer  parts  to  come  in  con- 
tact with  the  cooling*  substance. 

Q.  Does  BOILING  water  get  hotter  by  being 
KEPT  on  the  FIRE  1 

A.  No  : — not  if  the  steam  be  suffered 
to  escape. 

Q.  WHY  does  not  boiling  water  get  HOTTER. 
if  the  steam  be  suffered  to  ESCAPE  ? 

A.  Because  the  water  is  converted 
into  steam  as  fast  as  it  boils ;  and  the 
steam  carries  away  the  additional  heat. 

Q.  Why  does  SOUP  keep  HOT  longer  than  boil- 
ing water  ? 

A.  Because  the  grease  and  various  in- 
gredients floating- in  the  soup,  oppose  the 
ascending1  motion  of  the  hot  particles, 
and  prevent  their  rising-  so  freely  to  the 
surface. 

Q.  If  you  wanted  to  keep  WATER  HOT  for  a 
long  time,  how  could  it  be  done  ? 

A.  By  adding  a  little  starch  or  flour 
to  the  water. 

Q.  Why  would  a  little  STARCH,  added  to  boil- 
ing water,  serve  to  keep  it  HOT  ? 


216  COMMUNICATION    OF    HEAT. 

A.  Because  it  would  oppose  the 
ascending-  motion  of  the  hot  particles  of 
water,  and  prevent  their  rising  so  freely 
to  the  surface. 

Q.  Why  do  THICK  MILK,  RICE  MILK,  ^c.,  re- 
main HOT  longer  than  water  ? 

A.  Because  the  ascending*  motion  of 
the  hot  particles  is  opposed  by  the  flour 
or  rice,  and  cannot  so  quickly  reach  the 
surface. 

Q.      Is  STEAM  visible  or  INVISIBLE  ? 

A.  Steam  is  invisible;  but  when  it 
comes  in  contact  with  the  air  (being* 
condensed  into  small  drops)  it  instantly 
becomes  visible. 

Q.      How  do  you  know  that  STEAM  is  INVISIBLE  ? 

A.  If  you  look  at  the  spout  of  a  boil- 
ing- kettle,  you  will  find  that  the  steam 
(which  issues  from  the  spout)  is  always 
invisible  for  about  half  an  inch  ;  after 
which  it  becomes  visible. 

Q.  WHY  is  the  steam  INVISIBLE  for  HALF  AN 
INCH  ? 

A.  Because  the  air  is  not  able  to 
condense  it,  as  it  first  issues  from  the 
spout ;  but  when  it  spreads  and  comes  in 
contact  with  a  larger  volume  of  air,  the 
invisible  steam  is  readily  condensed  into 
visible  drops. 

Q.      WHY  do  STEAM-ENGINES  sometimes  BURST  ? 


HEATED    AIR.  217 

A.  Because  steam  is  very  elastic; 
and  this  elasticity  increases  in  a  greater 
proportion  than  the  heat  which  produces 
it ;  unless,  therefore,  some  vent  be  freely 
allowed,  steam  will  burst  the  vessel 
which  confines  it. 

Q.      Is  AIR  a  good  CONDUCTOR  ? 

A.  No;  air  is  a  very  bad  conductor; 
and  is  heated  (like  water)  by  convection. 

Q.       How  is  a  ROOM  WARMED  by  a  STOVE? 

A.  The  air  nearest  the  fire  is  made 
hot  first  and  rises ;  cold  air  then  descends, 
is  heated,  and  ascends  in  like  manner; 
and  this  interchange  goes  on  till  all  the 
air  of  the  room  is  warmed.  (Ste  p.  56.) 

Q.  Why  are  FIRES  placed  on  the  FLOOR  of  & 
room,  and  not  towards  the  CEILING  ? 

A.  Because  heated  air  always  as- 
cends. If,  therefore,  ihe  fire  were  not 
near  the  floor,  the  air  of  the  lower  part  of 
the  room  would  never  be  heated  by  the 
fire  at  all. 

Q.  If  you  take  a  POKER  out  of  the  fire,  and 
hold  the  HOT  END  DOWNWARDS,  why  is  the  HANDLE 
intensely  HOT'? 

A.     Because  the  hot  end  of  the  poker 
heats  the  air  around  it ;  and  this  hot  air 
(in  its  ascent)  scorches  the  poker  and  the 
hand  which  holds  it. 
10 


218  COMMUNICATION    OF    HEAT. 

Q.  How  should  a  RED-HOT  POKER  be  carried^ 
so  as  not  to  BURN  our  fingers? 

A.  With  the  hot  end  upwards;  for 
then  the  air  (heated  by  the  poker)  would 
not  pass  over  our  hand  and  scorch  it. 


PART    II. 


AIR. 


CHAPTER    XX. 

THE    ATMOSPHERE. 

Q.       Of  what  is  atmospheric  AIR  composed  ? 

A.  Principally  of  two  gases,  oxygen 
and  nitrogen,  mixed  together  in  the 
following  proportion:  viz.,  1  gallon  of 
oxygen  to  4  of  nitrogen. 

It  must  not  be  forgotten  that  the  air  contains  small 
quantities  of  other  gaseous  substances  also,  as  vapor  of 
water,  carbonic  acid,  and  ammonia. 

Q.       What  do  you  mean  by  a  GAS  ? 
A.     A  permanent  elastic  fluid  resem- 
bling air. 

N.  B.    MOST  GASES  ARE  INVISIBLE  OR  COLORLESS,  LIKE  AIR. 

"  PERMANENT," — In  this  respect  gas  differs  from  vapor, 
which  is  not  permanent;  for  vapor  may  be  easily  con- 
densed by  cold  into  a  liquid,  but  gas  never  changes  its 
gaseous  form.  . 

"  ELASTIC," — In  this  respect  gas  differs  from  a  liquid, 
which  is  almost  inelastic;  whereas  gas  is  exceedingly 
elastic. 

"RESEMBLING  AIR,"  or  aeriform. —  The  word  "Gas" 
means  air,  but  air  is  a  compound  of  two  gases.  Some 
few  gases  are  visible,  as  CHLORINE,  which  is  a  greenish 
yellow. 

219 


220  AIR. 


Q.       What  is  the  difference  between  a  GAS  and  a 


LIQUID 


A.     Gases  arc  elastic,  but  liquids  not. 

Q.  Illustrate  what  is  meant  by  "  the  ELASTICITY 
of  GAS." 

A.  If  from  a  vessel  full  of  gas  half 
were  taken  out  —  the  other  half  would  im- 
mediately spread  itself  out,  and  fill  the 
same  space  as  was  occupied  by  the  whole. 

Q.       Prove  that  a  LIQUID  is  NOT  ELASTIC. 

A.  If  from  a  gallon  of  water  you  take 
half,  the  remaining1  4  pints  will  take  up 
only  half  the  room  that  the  whole  gallon 
previously  did  :  a  liquid,  therefore,  is  not 
elastic  like  gas. 

Strictly  speaking,  a  liquid  is  slightly  elastic  ;  inasmuch 
as  it  may  be  compressed  and  will  afterwards  recover  its 
former  dimensions. 

Q.       What  are  the  uses  of  the  OXYGEN  of  the  air  ? 
A.     To  support  combustion  and  sus- 
tain life. 

Q.  What  is  meant,  when  it  is  said,  that  the 
OXYGEN  of  the  air  "SUPPORTS  COMBUSTION?" 

A.  It  means  this  :  It  is  the  oxygen 
of  the  air  which  makes  fuel  burn. 

Q.       How  does  the  OXYGEN  of  the  air  make  FUEL 


A.  The  fuel  is  decomposed  (by  heat) 
into  hydrogen  and  carbon;  and  these 
elements  combining  with  the  oxygen  of 
the  air  produce  combustion. 


GASES.  221 

Q.  What  GAS  is  produced  by  the  combination 
of  carbon  and  oxygen  ? 

A.     CARBONIC  ACID  GAS.     (/Steep.  43.) 

Q.  What  becomes  of  the  HYDROGEN  of  the 
FUEL  ? 

A.  The  hydrogen  of  the  fuel  combines 
with  the  oxygen  of  the  air,  and  forms 
WATERY  VAPOR  ;  but  the  combination  is 
attended  by  the  production  of  flame, 
owing*  to  the  very  inflammable  nature 
of  hydrogen  gas. 

Q.  What  becomes  of  the  NITROGEN  of  the  air, 
amidst  all  these  changes  and  combinations  ? 

A.  The  nitrogen  escapes  unchanged, 
to  be  again  mixed  with  oxygen,  and  con- 
verted into  common  AIR. 

Q.  What  is  meant,  when  it  is  said,  that  OXY- 
GEN "  SUSTAINS  LIFE  ?" 

A.  It  means  this :  If  a  person  could 
not  inhale  oxygen,  he  would  die. 

Q.  What  GOOD  does  this  inspiration  of  OXYGEN 
do? 

A.  1st — It  gives  vitality  to  the  blood  : 
and 

2dly — It  is  the  cause  of  animal  heat. 

Q.       How  is  FOOD  converted  into  BLOOD  ? 

A.  After  it  is  swallowed,  it  is  dis- 
solved in  the  stomach  into  a  grey  pulp, 
called  CHYME  ;  it  then  passes  into  the  in- 
testines, and  is  converted  by  the  "  bile" 
into  a  milky  substance,  called  CHYLE. 


222  AIR. 

Chyme — pronounce  kyme — chyle  pronounce  kyle — each 
as  one  syllable. 

Q.  What  BECOMES  of  the  milky  substance 
called  CHYLE  ? 

A.  It  is  absorbed  by  the  vessels  call- 
ed "  lacteals"  and  poured  into  the  veins 
on  the  left  side  of  the  neck. 

Lac'teals — -pronounce  Lac'-te-als. 
Q.       What   becomes   of  the   chyle,  AFTER  it  is 
POURED  into  the  VEINS  ? 

A.  It  mingles  with  the  blood,  and  is 
itself  converted  into  blood  also. 

Q.  How  does  the  OXYGEN  we  inhale  MINGLE 
with  the  BLOOD  ? 

A.  The  oxygen  of  the  air  mingles 
with  the  blood  in  the  lungs,  and  converts 
it  into  a  bright  red  color. 

Q.  What  color  is  the  blood  BEFORE  it  is  oxi- 
dized in  the  lungs  ? 

A.  A  dark  purple.  The  oxygen  turns 
it  to  a  bright  red. 

Oxidized,  i.  e.,  impregnated  with  oxygen. 

Q.  Why  are  PERSONS  so  PALE,  who  live  in 
CLOSE  ROOMS  and  CITIES  ? 

A.  Because  the  blood  derives  its 
redness  from  the  oxygen  of  the  air  inhal- 
ed ;  but,  as  the  air  in  close  rooms  and 
cities  is  not  fresh,  it  is  deficient  in  oxygen, 
and  cannot  turn  the  blood  to  a  beautiful 
bright  red. 

Q.  Why  are  PERSONS,  who  live  in  the  OPEN 
AIR  and  in  the  country,  of  a  RUDDY  complexion  ? 


BLOOD.  223 

A.  Because  they  inhale  fresh  air 
which  has  its  full  proportion  of  oxygen : 
and  the  blood  derives  its  bright  red  color 
from  the  oxygen  of  the  air  inhaled. 

Q.  Why  is  not  the  air  in  CITIES  so  FRESH  as 
that  i?i  the  COUNTRY? 

A.  Because  it  is  impregnated  with 
the  breath  of  its  numerous  inhabitants, 
the  odor  of  its  sewers,  the  smoke  of  its 
fires,  and  many  other  impurities. 

Q.  How  does  OXYGEN  convert  the  color  of  blood 
into  a  bright  RED? 

A.  The  coloring  matter  of  the  blood 
is  formed  by  very  minute  globules  float- 
ing in  it ;  the  oxygen  (uniting  with  the 
coats  of  these  globules)  makes  them  milky 
— and  the  dark  coloring  matter  of  the 
blood  (seen  through  this  'milky  coat) 
appears  of  a  bright  red. 

Exp. : — If  you  put  some  dark  venous  blood  into  a  milky 
glass,  and  hold  it  up  towards  the  light,  it  will  appear  of  a 
bright  florid  color  like  arterial  blood. 

Q.  How  does  the  COMBINATION  of  OXYGEN  with 
the  BLOOD  produce  animal  HEAT  ? 

A.  The  principal  element  of  the 
blood  is  carbon;  and  this  carbon  (com- 
bining with  the  oxygen  of  the  air  inhaled) 
produces  carbonic  acid  gas,  in  the  same 
way  as  burning  fuel.  (See  p.  43.) 

Q.  What  becomes  of  the  NITROGEN  of  the  air, 
after  the  oxygen  enters  the  blood  ? 


224  AIR. 

t 

A.  It  is  thrown  out  from  the  lungs 
unchanged,  by  the  act  of  breathing ;  to 
be  again  mixed  with  oxygen  and  con- 
verted into  common  AIR. 

Q.  Why  does  the  vitiated  air  (after  the  oxy- 
gen has  been  absorbed)  COME  OUT  of  the  MOUTH,  and 
not  sink  into  the  stomach  ? 

A.  Because  a  mechanical  provision 
is  made  in  the  upper  part  of  the  wind- 
pipe and  gullet  for  this  purpose. 

N.  B.  The  lungs  are  a  hollow,  spongy  mass,  capable  of 
confining  air  and  of  being  dilated  by  it.  They  are  so  situ- 
ated in  the  thorax  (or  chest),  that  the  air  must  enter  into 
them,  whenever  the  cavities  of  the  thorax  are  enlarged. 
The  process  of  breathing  is  performed  thus :  When  we 
INHALE,  the  thorax  (or  chest)  is  expanded ;  in  consequence 
of  which,  a  vacuum  is  formed  round  the  lungs,  and  heavy 
external  air  instantly  enters  (through  the  mouth  and 
throat)  to  supply  this  vacuum. 

When  we  EXHALE,  the  thorax  contracts  again ;  in  conse- 
quence of  which,  it  can  no  longer  contain  the  same  quan- 
tity of  air  as  it  did  before ;  and  some  of  it  is  necessarily 
expelled.  When  this  expulsion  of  air  takes  place,  the  lungs 
and  muscular  fibres  of  the  wind-pipe  and  gullet  contract,  in 
order  to  assist  the  process. 

Q.  If  (both  in  combustion  and  respiration)  the 
OXYGEN  of  the  air  is  CONSUMED,  and  the  NITROGEN 
REJECTED — Why  are  not  the  PROPORTIONS  of  the 

AIR  DESTROYED  ? 

A.  Because  the  under  surface  of  vege- 
table leaves  (during  the  day)  gives  out 
oxygen;  and  thus  restores  to  the  air  the 
very  element  of  which  it  has  been  de- 
prived. 


VEGETABLES.  225 

Q.  Whence  do  leaves  OBTAIN  the  oxygen 
which  they  exhale  ? 

A.  From  tfye  carbonic  acid  absorbed 
by  the  roots  from  the  soil,  and  carried  to 
the  leaves  by  the  rising*  sap. 

N.  B.    Carbonic  acid  (it  must  be  remembered)  is  a 
compound  of  carbon  and  oxygen. 

Q.      How  do  plants  contrive  to  absorb  carbonic 

acid  from  the  soil  ? 

A.  It  rises  (by  capillary  attraction) 
through  the  small  fibrous  roots,  after  it 
has  been  dissolved  in  the  soil  by  water. 

Q.       Whence  does  the  SOIL  obtain  carbonic  acid  ? 

A.  1st — From  the  air ;  from  which  it 
is  driven  by  falling  showers : 

2dly — From  the  decomposition  of  ve- 
g^etable  and  animal  matters,  which  al- 
ways produces  this  gas  in  abundance : 
and 

3dly — All  lime-stone,  chalk,  and  cal- 
careous stones,  contain  vast  quantities  of 
carbonic  acid  in  a  solid  state. 

Calcareous,  i.  e.3  of  a  limy  nature. 
Q.      If  leaves  throw  off  the  OXYGEN  of  the  car- 
bonic acid,  what  becomes  of  the  carbon? 

A.  It  is  retained  to  give  firmness  and 
solidity  to  the  plant  itself. 

Q.  Show  how  God  has  made  ANIMAL  life  de- 
pendent on  that  of  VEGETABLES. 

A.     Animals  require  oxygen  to  keep 
them  alive,  and  draw  it  from  the  air.  by 
10* 


226  AIR. 

inspiration  :  The  under  surface  of  leaves 
gives  out  oxygen  ;  and  thus  supplies  the 
air  with  the  very  gas  required  for  the 
use  of  animals. 

Q.  Show  how  God  has  made  VEGETABLE  life 
dependent  on  that  of  animal. 

A.  Plants  require  carbonic  acid, 
which  is  their  principal  food ;  and  all  an- 
imals exhale  the  same  gas  from  their 
lungs.  Thus  plants  supply  animals  with 
oxygen,  and  animals  supply  plants  with 
carbonic  acid. 

Q.         HOW  is  AIR  HEATED  ? 

A.     By  "convective  currents." 

Q.      Explain  what  is  meant  by  "  CONVECTIVE 

CURRENTS." 

A.  When  a  portion  of  air  is  heated, 
it  rises  upwards  in  a  current,  carrying 
the  heat  with  it ;  other  colder  air  succeeds, 
and  (being  heated  in  a  similar  way)  as- 
cends also  :  TEhese  are  called  "  convective 
currents." 

("  Convective  currents  ;"  so  called  from  the  Latin  words, 
cum-vectus  (earned  with)]  because  the  heat  is  "carried 
with  "  the  current.) 

Q.      Is  AIR  HEATED  by  the  RAYS  of  the  SUN  ? 

A.  No  ;  air  is  not  heated  (in  any  sen- 
sible degree)  by  the  action  of  tlie  sun's 
rays  passing  through  it. 

Q.  Why  then  is  the  AIR  HOTTER  on  a  SUNNY 
DAY,  than  on  a  CLOUDY  one  ? 


CONVECTION.  227 

A.  Because  the  sun  heats  the  surface 
of  the  earth,  and  the  air  (resting-  on  the 
earth)  is  heated  by  contact :  as  soon  as  it 
is  heated  it  ascends ;  while  its  place  is 
supplied  by  colder  portions  which  are 
heated  in  turn  also. 

Q.  If  AIR  be  a  BAD  CONDUCTOR,  why  does  hot 
IRON  become  COLD  by  EXPOSURE  to  the  AIR  ? 

A.  Because  it  is  made  cold — 1st — 
By  "  convection  ;"  and  2dly — By  "  radi- 
ation." 

Q.       How  is  hot  iron  made  cold  by  CONVECTION  ? 

A.  The  air  resting  on  the  hot  iron 
(being-  intensely  heated),  rapidly  ascends 
with  the  heat  it  has  absorbed  ;  colder  air 
succeeding1  absorbs  more  heat  and  as- 
cends also ;  and  this  process  is  repeated 
till  the  hot  iron  is  cooled  completely  down. 

Q.       How  is  hot  iron  cooled  by  RADIATION  ? 

A.  While  its  heat  is  being-  carried  off 
by  "  convection/'  the  hot  iron  throws  off 
heat  (on  all  sides)  by  radiation  also. 

Q.       What  is  meant  by  RADIATION  ? 

A.  Heat  emitted  (in  all  directions) 
from  any  surface  by  rays. 

Q.  How  is  BROTH  COOLED  by  being  left  ex- 
posed to  the  AIR  ? 

A.  It  throws  off  some  heat  by  radia- 
tion ;  but  it  is  mainly  cooled  down  by 
convection. 


228  AIR. 

Q.  How  is  hot  BROTH  cooled  down  by  CONVEC- 
TION 'I 

A.  The  air  resting  on  the  hot  broth 
(being  heated)  ascends ;  colder  air  suc- 
ceeding* absorbs  more  heat,  and  ascends 
also ;  and  this  process  is  repeated  till 
the  broth  is  made  cool. 

The  particles  on  the  surface  of  the  broth  sink  as  they 
are  cooled  down,  and  warmer  particles  rise  to  the  surface  ; 
which  gradually  assists  the  cooling  process. 

Q.  Why  is  hot  TEA  and  BROTH  COOLED  faster 
by  being  STIRRED  about  ? 

A.  1st — Because  the  agitation  assists 
in  bringing  its  hottest  particles  to  the 
surface. 

2dly — The  action  of  stirring  agitates 
the  air,  and  brings  it  more  quickly  to  the 
broth  or  tea :  and 

3dly — As  the  hotter  particles  are  more 
rapidly  brought  into  contact  with  the 
air,  therefore,  convection  is  more  rapid. 

Blowing  tea  or  broth  cools  it  also.     (See  p.  168.) 
Q.       If  a  shutter  be  closed  in  the  day-time,  the 
stream  of  light  (piercing  through  the  crevice)  seems 

in  CONSTANT  AGITATION.       WflY  is  this  ? 

A.  Because  little  motes  arid  particles 
of  dust  (thrown  into  agitation  by  the 
violence  of  the  convective  currents)  are 
made  visible  by  the  strong  beam  of  light 
thrown  into  the  room  through  the  cre- 
vice of  the  shutter. 


PRESSURE    OP    AIR.  229 

Q.  Why  is  the  GALLERY  of  a  CHURCH  or  the- 
atre HOTTER  than  the  AISLE  or  'pit  ? 

A.  Because  the  hot  air  ascends  from 
the  bottom  to  the  top  of  tlie  building  ; 
while  cold  air  flows  to  the  bottom  from 
the  doors  and  windows. 

Q.  Why  do  persons  who  ascend  in  balloons 
feel  intense  pain  in  their  eyes  and  ears  ? 

A.  Because  the  air  of  the  upper 
regions  is  more  rarefied  than  that  on  the 
earth ;  and  the  air  inside  their  bodies 
(seeking-  to  become  of  the  same  rarity) 
bursts  through  their  eyes  and  ears,  pro- 
ducing* intense  pain. 

Q.       Why  is  it  often  PAINFUL  and  difficult  to 

BREATHE,  On  a  MOUNTAIN-TOP  ? 

A.  Because  the  pressure  of  air  on  the 
mountain-top  is  not  so  great  as  it  is  on 
the  plain;  and  the  air  inside  our  bodies 
(seeking  to  become  of  the  same  rarity) 
bursts  through  the  pores  of  the  body  and 
produces  great  pain. 

Q.  Why  do  we  feel  OPPRESSED  just  PREVIOUS 
to  a  storm  ? 

A.  Because  the  air  is  greatly  rarejied 
by  heat  and  vapor ;  and  the  air  inside  us 
(seeking  to  become  of  the  same  rarity) 
produces  an  oppressive  and  suffocating 
feeling. 


230  AIR. 

Q.  Why  do  DIVERS,  when  they  a>'e  under 
water,  suffer  great  pain  in  their  eyes  and  ears  ? 

A.  Because  the  air  at  the  bottom  of 
the  sea  is  more  dense  than  the  air  on  the 
surface ;  and  (till  the  air  inside  the  diver's 
body  is  settled  into  the  same  density)  he 
feels  oppressed  with  pain,  especially  in 
the  ears. 

Q.       Why  is  this  PAIN  felt  especially  about  the 

EARS  of  a  DIVER  ? 

A.  Because  the  ear  is  fitted  with  a 
small  membrane  called  the  e/raw(ortym'- 
panum),  through  which  the  dense  air 
bursts:  The  rupture  of  this  membrane 
very  often  produces  incurable  deafness. 

When  the 'diver  is  not  in  a  bell  the  dense  water  bursts 
into  his  ears  and  ruptures  the  tympanum. 

Q.       Why  do  our  CORNS  ache  just  previous  to 

RAIN  ? 

A.  Because  our  feet  swell  from  the 
sudden  depression  in  the  density  of  air ; 
and  the  hard  corn  (not  being  elastic)  is 
painfully  stretched  and  pressed. 

Some  of  this  pain  is  due  to  electricity. 

Q.  How  do  you  know  that  the  density  of  the 
air  is  lowered,  previous  to  a  storm  ? 

A.  Because  the  mercury  of  a  barome- 
ter rapidly  falls. 

Q.       Why  do  CELLARS  feel  WARM  in  WINTER  ? 

A.     Because  the  external  air  has  not 


RUST.  231 

free  access  into  them ;  in  consequence  of 
which,  they  remain  almost  at  an  even 
temperature — which  (in  winter  time)  is 
about  10  degrees  warmer  than  the  ex- 
ternal air. 

Q.       Why  do  CELLARS/^  COLD  in  SUMMER? 

A.  Because  the  external  air  has  not 
free  access  into  them  ;  in  consequence 
of  which,  they  remain  almost  at  an  even 
temperature — which  (in  summer  time)  is 
about  10  degrees  colder  than  the  exter- 
nal air. 

Q.       Why  does  AIR  rust  IRON  ? 

A.  Because  the  oxygen  of  the  air 
combines  with  the  surface  of  the  metal, 
and  produces  oxide  of  iron;  which  is 
generally  called  "  rust." 

An  oxide  of  iron,  copper,  &c.,  is  oxygen  in  combination 
with  iron,  copper,  &c. 

Q.  Why  does  hot  iron  SCALE  and  PEEL  off^ 
when  ,struck  with  a  HAMMER? 

A.  Because  the  oxygen  oftJie  air  very 
readily  unites  with  the  surface  of  the 
hot  iron,  and  forms  a  metallic  oxide  (or 
rust),  which  scales  off  when  struck  with 
a  hammer. 

Q.      Does  iron  RUST  in  DRY  air  ? 
A.     No;    iron  undergoes  no  change 
in  dry  air. 


232  AIR. 

Q.  Why  do  STOVES  and  FIRE-IRONS  become 
RUSTY  in  rooms,  which  are  riot  OCCUPIED  ? 

A.  Because  the  air  is  damp;  and 
moist  air  oxidizes  iron  and  steel. 

Oxidizes,  i.  e.,  rusts. 

Q.  In,  what  part  of  the  year  is  it  most  difficult 
to  keep  STOVES  and  FIRE-IRONS  BRIGHT? 

A.     In  autumn  and  winter. 

Q.  Why  is  it  more  difficult  to  keep  STOVES  and 
FIRE-IRONS  bright  in  AUTUMN  and  WINTER  than  in 
spring  and  summer  ? 

A.  Because  the  capacity  of  the  air 
for  holding*  water  is  constantly  on  the 
decrease,  after  the  summer  is  over ;  in 
consequence  of  which,  vapor  is  deposited 
on  everything  with  which  the  air  comes 
in  contact. 

Q.  Why  does  GREASING  iron  prevent  its  be- 
coming RUSTY  ? 

A.  Because  grease  prevents  the  hu- 
midity of  air  from  coming*  in  contact 
with  the  surface  of  the  iron. 

Q.  Why  do  not  STOVES  rust  so  frequently  as 
POKERS  and  TONGS  ? 

A.  Because  stoves  are  generally  cov- 
ered with  plumbago,  or  black  lead. 

Q.       W^hat  is  plumbago^  or  black  lead  ? 

A.     A  mixture  of  charcoal  and  iron. 

Plumbago  (strictly  speaking)  is  a  chemical  union  of 
caibon  and  iron,  in  the  following  proportions: — 91  parts 
carbon  and  9  iron.  But  the  BLACK  LEAD  sold  in  shops  is  a 
mixture  of  charcoal  and  iron  filings. 


METALS.  233 

N.  B.  A  most  excellent  varnish  to  prevent  rust  is 
made  of  1  pint  of  fat  oil  varnish,  mixed  with  5  pints  of 
highly  rectified  spirits  of  turpentine,  rubbed  on  the  iron 
or  steel  with  a  piece  of  sponge.  This  varnish  may  be  ap- 
plied to  bright  stoves,  and  even  mathematical  instruments, 
without  injuring  their  delicate  polish. 

Q.  Why  does  ornamental  STEEL  (of  a  purple 
or  LILAC  color)  rust  more  readily  than  polished 
WHITE  steel  ? 

A.  Because  the  lilac  tinge  is  pro- 
duced by  partial  oxidation;  and  the 
process  which  forms  rusts  has,  therefore, 
already  commenced. 

Q.  How  can  lilac  STEEL  be  kept  FREE  from 
RUST  ? 

A.     By  keeping-  it  in  a  very  dry  place. 

Q.  If  DRY  AIR  contains  OXYGEN,  why  does  it 
NOT  RUST  IRON,  as  well  as  MOIST  air  ? 

A.  Because  moisture  is  always  need- 
ed, in  order  to  bring*  into  action  the 
affinity  of  oxygen  for  steel. 

Q.  Do  any  OTHER  metals  (besides  iron)  com- 
bine rapidly  with  oxygen  ? 

A.  Yes ;  copper,  lead,  mercury,  and 
even  silver  to  some  extent. 

Q.       Why  does  COPPER  TARNISH  ? 

A.  The  tarnish  of  copper  is  caused 
by  its  oxidation :  that  is,  the  oxygen  of 
the  air  combines  with  the  surface  of  the 
copper,  and  (instead  of  rusting  it)  covers 
it  with -a  dark  tarnish. 

Q.  Why  does  LEAD  become  of  a  DARKER  hue, 
by  being  exposed  to  the  air  ? 


234  AIR. 

A.  Because  the  vapor  of  the  air  com- 
bines with  the  lead,  and  oxidizes  its  sur- 
face ;  but  instead  of  becoming-  rusty,  the 
surface  assumes  a  darker  hue. 

Q.  Why  does  LEAD  lose  its  BRIGHTNESS,  and 
become  DULL,  by  being  exposed  to  the  air  ? 

A.  The  dullness  of  the  lead  is  caused 
by  the  presence  of  a  carbonate  of  the 
oxide.  When  the  oxide  is  formed,  it 
attracts  carbonic  acid  from  the  air,  and 
(combining1  with  it)  produces  a  carbonate, 
which  gives  the  dull  tint  to  old  lead. 

Q.       Why  is  it  difficult  to  keep  SILVER  BRIGHT  1 

A.  Because  the  vapor  of  the  air  oxi- 
dizes its  surface,  and  tarnishes  it. 

Q.  Why  do  silver  TEA-POTS  and  SPOONS  tar- 
nish more  quickly  than  silver  ore  or  bullion  ? 

A.  Because  alloy  of  some  baser  me- 
tal is  used,  to  make  them  more  hard  and 
lasting ;  and  this  alloy  oxidizes  more 
quickly  than  silver  itself. 

Q.  Why  does  GERMAN  silver  turn  a  dingy 
yelloio  in  a  few  hours  ? 

A.  Because  German  silver  has  a 
great  affinity  for  oxyg*en  ;  and  shows  its 
oxidation  by  a  sickly  yellow  tarnish,  in- 
stead of  rust. 

Q.  If  quicksilver  (or  mercury)  will  tarnish  lik 
copper  and  lead — why  does  it  preserve  its  BRILLIANCY 
in  BAROMETERS  and  THERMOMETERS  ? 


OXIDATION — PLATINUM.  235 

A.  Because  the  air  is  excluded  ;  and 
no  moisture  can  come  in  contact  with  it, 
to  oxidize  (or  tarnish)  it. 

Q.       Is  GOLD  affected  by  the  atmosphere  ? 

A.  Not  readily ;  gold  will  never 
combine  with  oxygen  of  itself,  (i.  e., 
without  aid.) 

Q.  WHICH  of  the  METALS  is  capable  of  resisting 
oxidation  altogether  ? 

A.  Plat'inum ;  in  consequence  of 
which,  the  graduated  arcs  of  delicate 
"  instruments-for-observation  "  are  made 
of  plat'inum  instead  of  any  other  metal. 

Q.  Why  is  PLAT'INUM  used  for  the  graduated 
arcs  of  delicate  mathematical  instruments^  instead  of 
any  other  metal  ? 

A.  Because  it  will  never  oxidize; 
but  retains  its  bright  surface  in  all  wea- 
thers, free  from  both  rust  and  tarnish. 

Q.  Before  plat'inum  was  discovered,  which  of 
the  metals  was  employed  for  the  same  purpose  ? 

A.     Gold. 

Plat'inum  (a  white  metal),  so  called  from  "  plata," 
the  Spanish  •  word  for  silver.  It  was  introduced  from 
South  America  into  England  hy  Mr.  Wood,  (A.  D.  1749.) 

Q.  For  what  other  SCIENTIFIC  purpose  is  PI&T'- 
INUM  now  used  ? 

A.  For  crucibles  in  which  acids  are 
employed  :  and  for  galvanic  batteries. 

Q.  Why  are  CRUCIBLES  (in  which  acids  are 
employed)  made  of  PLAT'INUM  ? 


236  AIR. 

A.  Because  the  acid  would  act  upon 
other  metals,  or  upon  glass ;  and  prevent 
the  experimenter's  success. 

Q.  Which  of  the  METALS  have  the  GREATEST 
affinity  for  OXYGEN? 

A.  Those  called  potas'sium  and  so- 
dium. 

Potassium  and  so'dium  derive  their  names  from  potash 
and  soda.  Potas'sa  is  the  oxide  of  potas'sium  ;  and  soda 
is  the  oxide  of  so'dium. 

Q.  How  is  the  affinity  of  potas'sium  and  so- 
dium for  oxygen  shown  ? 

A.  They  decompose  water  immediately 
they  are  brought  into  contact  with  it. 

Q.       What  EFFECT  has  POTAS'SIUM  on  WATER  ? 

A.  It  catches  fire  the  moment  it  is 
thrown  into  water,  and  burns  with  a 
vivid  flame — which  is  still  further  in- 
creased by  the  combustion  of  hydrogen, 
separated  from  the  water. 

N.  B.  Water  is  composed  of  oxygen  and  hydrogen ; 
and  potas'sium  separates  the  two  gases. 

Q.       What  effect  has  SO'DIUM  on  WATER  1 
A.     It  does  not  take^re,  as  potassium 
does ;  but  undergoes  very  rapid  oxida- 
tion. 

Q.       Is  the  FURR  of  KETTLES  an  oxide  ? 

A.  No  ;  the  furr  (or  deposit  of  boil- 
ing water)  is  a  precipitate  of  lime  and 
mineral  salt,  separated  from  the  water 
by  the  process  of  boiling. 


FURR.  237 

Q.       Is   not  this   FURR  of  lolling    water  often 

DANGEROUS  1 

A.  Yes  ;  especially  in  tubular  boilers, 
such  as  those  employed  in  railways. 

Q.  Why  is  this  FURR  especially  TROUBLESOME 
in  RAILWAY  engines  ? 

A.  Because  it  is  a  bad  conductor  of 
heat;  in  consequence  of  which,  it  hin- 
ders the  evaporating  effect  of  the  fire, 
and  prevents  the  economy  of  fuel. 

Q.  Why  is  this  FURR  especially  DANGEROUS 
in  RAILWAY  engines  ? 

A.  Because,  when  it  is  deposited  in 
the  boilers,  they  are  likely  to  become 
over-heated;  and  then  explosion  will  take 
place,  from  the  sudden  generation  of 
highly  elastic  steam. 

Q.       Why  cannot  RAILWAY  engines  be  fed  with 

BRACKISH  WATER  ? 

A.  Because  brackish  water  contains 
mineral  salt ;  which  makes  a  much  lar- 
ger deposit  of  furr  than  water  which 
contains  only  vegetable  matters. 


238  CARBONIC    ACID    GAS. 


CARBONIC  ACID  GAS. 

CHAPTER  XXL 

Q.       What  is  CARBONIC  ACID  GAS  ? 
A.     A  gas  formed  by  the   union   of 
carbon  and  oxygen  :  It  used  to  be  called 

"  FIXED  AIR." 

3  Ibs.  of  carbon  and  8  Ibs.  of  oxygen  will  form  11  Ibs.  of 
carbonic  acid. 

Q.  Under  what  circumstances  does  CARBON 
most  readily  UNITE  with  OXYGEN  ? 

A.  1st  —  When  its  temperature  is 
raised :  Thus  if  carbon  be  red-hot,  oxy- 
gen will  most  readily  unite  with  it  : 
and 

2dly — When  it  forms  part  of  the  fluid 
blood. 

Q.  Why  do  oxygen  and  carbon  so  readily 
unite  in  the  BLOOD  ? 

A.  Because  the  atoms  of  carbon  are 
so  loosely  attracted  by  the  other  materials 
of  the  blood,  that  they  unite  very  readily 
with  the  oxygen  of  the  air  inhaled. 

Q.       Is  carbonic  acid  WHOLESOME  ? 

A.  No;  it  is  fatal  to  animal  life; 
and  (whenever  it  is  inhaled)  acts  like  a 
narcotic  poison — producing  drowsiness, 
which  sometimes  ends  in  death. 

Q.  How  can  any  one  KNOW,  if  a  place  be  in* 
fested  with  CARBONIC  ACID  GAS  ? 


VITIATED   AIR.  239 

A.  If  a  pit  or  well  contain  carbonic 
acid,  a  candle  (let  down  into  it)  will  be 
insUmthj  extinguished.  The  rule,  there- 
fore, is  this — Where  a  candle  will  burn, 
a  man  can  live ;  but  what  will  extinguish 
a  candle,  will  also  destroy  life. 

Q.  Why  does  a  MINER  lower  a  CANDLE  into 
a  mine,  before  he  descends  ? 

A.  Because  the  candle  will  be  extin- 
guished, if  the  mine  contains  carbonic 
acid  gas :  but  if  the  candle  is  not  extin- 
guished, the  mine  is  safe,  and  the  man 
may  fearlessly  descend. 

Q.       Why  does    a    CROWDED    ROOM    produce 

HEAD-ACHE  ? 

A.  Because  we  breathe  air  vitiated 
by  the  crowd. 

Q.       Why  is  the  AIR  of  a  room  VITIATED  by  a 

CROWD  ? 

A.  Because  it  is  deprived  of  its  due 
proportion  of  oxygen,  and  laden  with 
carbonic  acid. 

Q.  How  is  the  air  of  a  room  affected  thus  by 
a  crowd  ? 

A.  The  elements  of  the  air  inhaled 
are  separated  in  the  lungs  : — the  oxygen 
is  converted  in  the  blood  into  carbonic 
add;  and  the  carbonic  acid  (together 
with  the  nitrogen)  is  thrown  back  again 
by  the  breath  into  the  room. 


240  CARBONIC    ACID    GAS. 

Q.         Is     ALL     the    NITROGEN     REJECTED     by    the 


_   t? 

A.  Yes ;  all  the  nitrogen  of  the  air 
is  always  expired. 

Q.       Why  is  a  CROWDED  ROOM  UNWHOLESOME  ? 

A.  Because  the  oxygen  of  the  air  is 
absorbed  by  the  lungs;  and  carbonic 
acid  gas  (which  is  a  noxious  poison)  is 
substituted  for  it. 

Q.  Mention,  the  historical  circumstances,  so 
well  known  in  connexion  with  the  "  BLACK  HOLE 
of  CALCUTTA." 

A.  In  the  reign  of  George  II.,  the 
Raja  (or  Prince)  of  Bengal*  marched 
suddenly  to  Calcutta,  to  drive  the  Eng- 
lish from  the  country  ;  as  the  attack  was 
unexpected,  the  English  were  obliged 
to  submit,  and  146  persons  were  taken 
prisoners. 

Q.       What  became  of  these  prisoners  ? 

A.  They  were  driven  into  a  place 
about  18  feet  square,  and  15  or  16  feet 
in  height,  with  only  two  small  grated 
windows.  123  of  the  prisoners  died  in 
one  night ;  and  (of  the  23  who  survived) 
the  larger  portion  died  of  putrid  fevers, 
after  they  were  liberated. 

Q.       Why  were  so  many  persons  SUFFOCATED  in 

*  The  Sur  Raja,  at  Dowlat ;  a  young  man  of  violent  pas- 
sions, who  had  but  just  succeeded  to  the  throne.  A.  D.  1756. 


JUNGLES.  241 

«&  few  hours,  from  confinement  in  this  dose,  hot  PRIS- 
ON-HOLE ? 

A,  Because  the  oxygen  of  the  air  was 
soon  consumed  by  so  many  lungs,  and 
its  place  supplied  by  carbonic  acid,  ex- 
haled by  the  hot  breath. 

Q.  ~tffhy  did  the  captives  in  the  BLACK  HOLE 
die  SLEEPING? 

Ar  1st— Because  the  absence  of  oxy- 
gen quickly  affects  the  vital  functions, 
depresses  the  nervous  energies,  and  pro- 
duces a  lassitude  which  ends  in  death : 
and 

2dly  —  Carbonic  acid  gas  (being  a 
narcotic  poison)  produces  drowsiness  and 
death,  in  those  who  inhale  it. 

Q.  Why  are  the  JUNGLES  of  Java  and  Hin- 
dostan  so  FATAL  to  life  ? 

A.  Because  vast  quantities  of  car- 
bonic acid  are  thrown  off  by  decaying 
vegetables  in  these  jungles ;  and  (as  the 
wind  cannot  penetrate  the  thick  brush- 
wood to  blow  the  pernicious  gas  away) 
it  settles  there,  and  destroys  animal  life. 

Q.  Why  do  persons  in  a  crowded  CHURCH  feel 
DROWSY  ? 

A.     1st — Because  the  crowded  con- 
gregation inhale  a  large  portion  of  the 
oxygen  of  the  air,  which  alone  can  sus- 
tain vitality  and  healthy  action  :  and 
11 


242  CARBONIC    ACID    GAS. 

2dly — The  air  of  the  church  is  im- 
pregnated with  carbonic  acid  gas,  which 
(being-  a  strong  narcotic)  produces  drow- 
siness in  those  who  inhale  it. 

Q.  Why  do  PERSONS  who  are  much  in  the 
OPEN  AIR  enjoy  the  best  HEALTH  ? 

A.  Because  the  air  they  inhale  is 
much  more  pure. 

Q.  Why  is  COUNTRY  AIR  more  PURE  than  the, 
air  in  CITIES  ? 

A.  1st — Because  there  are  fewer 
inhabitants  to  vitiate  the  air  : 

2dly — There  are  more  trees  to  restore 
the  equilibrium  of  the  vitiated  air :  and 

3dly — The  free  circulation  of  air 
keeps  it  pure  and  wholesome  :  (In  the 
same  way  as  running  streams  are  pure 
and  wholesome,  while  stagnant  waters 
are  the  contrary.) 

Q.  Why  does  the  SCANTINESS  of  a  country 
POPULATION  render  the  COUNTRY  AIR  more  PURE  1 

A.  Because  the  fewer  the  inhabitants, 
the  less  carbonic  acid  will  be  exhaled; 
and  thus  country  people  inhale  pure 
oxygen,  instead  of  air  impregnated  with 
the  narcotic  poison,  called  carbonic  acid 
gas. 

Q.  Why  do  TREES  and  FLOWERS  help  to  make 
country  AIR  WHOLESOME  ? 

A.     1st — Because  trees  and  flowers 


COUNTRY    AND    CITY    AIR.  243 

absorb  the  carbonic  acid,  generated  by 
the  lungs  of  animals,  putrid  substances, 
and  other  obnoxious  exhalations  :  and 

2dly — Trees  and  flowers  restore  to 
the  air  the  oxygen,  which  has  been 'in- 
haled by  man  and  other  animals. 

Q.  Why  is  the  AIR  of  CITIES  LESS  wholesome, 
than  COUNTRY  air  ? 

A.  1st — Because  there  are  more  in- 
habitants  to  vitiate  the  air : 

2dly — The  sewers,  drains,  bins,  and 
filth  of  a  city,  very  greatly  vitiate  the 
air: 

3dly — The  streets  and  alleys  prevent 
a  free  circulation  :  and 

4thly — There  are  fewer  trees  to  ab- 
sorb the  excess  of  carbonic  acid  gas, 
and  restore  the  equilibrium. 

Q.  Why  are  PERSONS,  who  live  in  CLOSE 
ROOMS  and  crowded  CITIES,  generally  SICKLY  ? 

A.  Because  the  air  they  breathe  is 
not  pure,  but  is  (in  the  1st  place)  defec- 
tive in  oxygen;  and  (in  the  2d)  is  im- 
pregnated with  carbonic  acid  gas. 

Q.  Where  does  the  CARBONIC  ACID  of  close 
ROOMS  and  CITIES  COME  from? 

A.  From  the  lungs  of  the  inhabitants, 
the  sewers,  drains,  and  other  like  places, 
in  which  organic  substances  are  under- 
going decomposition. 


244  CARBONIC    ACID    GAS. 

Q.  What  BECOMES  of  the  CARBONIC  ACID  of 
crowded  cities  ? 

A.  Some  of  it  is  abswbed  by  vegeta- 
bles ;  and  the  rest  is  blown  away  by  the 
wind,  and  diffused  through  the  whole 
volume  of  the  air. 

Q.  Does  not  this  constant  diffusion  of  carbonic 
acid  affect  the  PURITY  of  the  WHOLE  AIR  ? 

A.  No ;  because  it  is  wafted  by  the 
wind  from  place  to  place,  and  absorbed 
in  its  passage  by  the  vegetable  world. 

Q.  '  ""What  is  CHOKE  DAMP? 

A.  Carbonic  acid  gas  accumulated  at 
the  bottom  of  wells  and  pits,  which  ren- 
ders them  noxious,  and  often  fatal  to 
life. 

Q.  Why  is  not  this  carbonic  acid  TAKEN  UP  by 
the  AIR  and  DIFFUSED,  as  it  is  in  cities  ? 

A.  Because  (being  heavier  than  com- 
mon air)  it  cannot  rise  from  the  well  or 
pit :  and  no  wind  can  get  to  it,  to  blow 
it  away. 

Q.  Why  are  PERSONS  sometimes  KILLED  by 
leaning  over  BEER  VATS  ? 

A.  Because  vats  (where  beer  has 
been  made)  contain  a  large  quantity  of 
carbonic  acid  gas,  produced  by  the  "  vi- 
nous fermentation"  of  the  beer ;  and 
when  a  man  incautiously  leans  aver  a 


BEER    VATS — CHARCOAL.  245 

beer  vat,  and  inhales  the  carbonic  acid, 
he  is  immediately  killed  thereby. 

Q.  Why  are  PERSONS  often  KILLED,  who  enter 
BEER  VATS  to  clean  them? 

A.  Because  carbonic  acid  (being*  hea- 
vier than  atmospheric  air}  often  rests  upon 
the  bottom  of  a  vat :  when,  therefore,  a 
person  enters  the  vat,  and  stoops  to  clean 
the  bottom,  he  inhales  the  pernicious  gas, 
which  kills  him. 

Q.  Why  are  PERSONS  sometimes  KILLED,  by 
.having  a  CHARCOAL  FIRE  in  their  bedrooms  ? 

A.  Because  the  carbon  of  the  burning 
charcoal  unites  with  the  oxygen  of  the  air, 
and  forms  carbonic  acid  gas,  which  is  a 
narcotic  poison. 

Q.  If  carbonic  acid  settles  at  the  BOTTOM  of  a, 
room,  how  can  it  injure  a  person  LYING  upon  a  BED, 
raised  considerably  above  the  jioqf  ? 

A.  Because  all  gases  diffuse  them- 
selves through  each  other,  as  a  drop  of 
ink  would  diffuse  itself  through  a  cup  of 
water.  If,  therefore,  a  person  slept  for 
6  or  8  hours  in  a  room  containing  carbonic 
acid,  quite  enough  of  the  gas  will  be 
diffused  throughout  the  room  to  produce 
death. 

The  heat  of  the  fire  assists  the  process  of  diffusion. 
Q.       What  are  the  chief  SOURCES  of  CARBONIC 
ACID? 


246  CARBONIC    ACID    GAS. 

A.     1st — The  breath  of  animals. 

2dly — The  decomposition  of  vegetable 
and  animal  matter. 

3dly — Lime-stone,  chalk,  and  all  cal- 
careous stones, — in  which  it  exists  in  a 
solid  form. 

Q.  From  which  of  these  sources  is  CARBONIC 
ACID  most  likely  to  ACCUMULATE  to  a  noxious  extent  ? 

A.  From  the  fermentation  and  putre- 
faction of  decaying  vegetable  and  ani- 
mal matters. 

Q.       How  can  this  ACCUMULATION  of  CARBONIC 

ACID  be  PREVENTED? 

A.  By  throwing  quick-lime  into  pla- 
ces, where  such  fermentation  and  pu- 
trefaction are  going  on. 

Q.         HOW    Will    QUICK-LIME    PREVENT    the   OCCU- 

mulation  of  CARBONIC  ACID  ? 

A.  Quick-lime  will  absorb  the  car- 
bonic acid  ;  and  produce  a  combination 
called  "  carbonate  of  lime.77 

Q.  Does  not  heavy  RAIN  prevent  the  ACCUMU- 
LATION of  CARBONIC  ACID,  as  well  as  quick-lime  ? 

A.  Yes ;  an  abundant  supply  of 
water  will  prevent  the  accumulation  of 
carbonic  acid,  by  dissolving  it. 

N.  B.  Red  heat  (as  a  pan  of  red-hot  coals,  or  a  piece 
of  red-hot  iron)  will  soon  absorb  the  carbonic  acid  gas, 
accumulated  in  a  pit  or  well. 

Q.  What  effect  has  CARBONIC  ACID  on  the  WA- 
TER in  which  it  is  dissolved  ? 


EFFERVESCENCE.  247 

A..  It  renders  it  slightly  acid  to  the 
taste. 

Q.  Can  the  CAPACITY  of  water  for  dissolving 
carbonic  acid  be  increased  ? 

A.  Yes.  Carbonic  acid  may  be  forced 
into  water  by  pressure  to  a  considerable 
extent. 

Q.  To  what  practical  USES  has  this  capacity 
of  water  (  for  dissolving  carbonic  acid)  been  applied  ? 

A.  Effervescing  draughts  are  made 
upon  this  principle. 

Q.  Explain  the  cause  of  EFFERVESCENCE  in 
these  beverages  ? 

A.  The  carbonic  acid  of  the  beverage 
(being-  prevented  by  the  cork  from  es- 
caping] is  forced  into  the  liquor  by  pres- 
sure, and  absorbed  by  it:  but  when  the 
cork  (or  pressure)  is  removed,  some  of 
the  carbonic  acid  flies  off  in  bubbles  or 
effervescence. 

Q.  Why  does  AERATED  WATER  effervesce  when 
the  CORK  is  removed  ? 

A.  While  the  bottle  remains  cork- 
ed, carbonic  acid  is  forced  into  the  water 
by  pressure,  and  absorbed  by  it :  but, 
when  the  cork  (or  pressure)  is  removed, 
some  of  the  carbonic  acid  flies  off  in 
effervescence. 

Q.       Why  does  SODA  WATER  effervesce  ? 

A.     In  soda  water  there  is  forced  8 


248  CARBONIC    ACID    GAS. 

times  its  own  bulk  of  carbonic  acid  gas, 
which  makes  its  escape  in  effervescence, 
as  soon  as  the  cork  is  removed. 

Q.  Why .  does  GINGER  POP  fly  about  in  froth, 
when  the  string  of  the  cork  is  cut  ? 

A.  Because  it  contains  carbonic  acid 
gas.  While  the  cork  is  fast,  the  carbonic 
acid  is  forced  into  the  liquor  ;  but  when 
the  pressure  is  removed  the  gas  is  given 
off  in  effervescence. 

N.  B.  All  vinous  fermentation  produces  carbonic  acid. 
Q.       Why  does  BOTTLED  ALE  froth  more  than 
DRAUGHT  ale  ? 

A.  Because  the  pressure  is  greater 
in  a  bottle  than  in  a  tub  which  is  contin- 
ually tapped ;  and  effervescence  is  al- 
ways increased  by  pressure. 

Q.  What  produces  the  FROTH  of  BOTTLED 
PORTER  ? 

A.  Carbonic  acid  generated  by  the 
vinous  fermentation  of  the  porter  :  This 
gas  is  absorbed  by  the  liquor,  so  long  as 
the  bottle  is  well  corked  ;  but  is  given  off 
in  froth,  when  the  pressure  of  the  cork  is 
removed. 

Q.  What  gives  the  pleasant  ACID  taste  to  soda 
water,  ginger  beer,  champagne,  and  cider  ? 

A.  The  presence  of  carbonic  acid, 
generated  by  fermentation ;  and  liberal- 


SPRING  WATER — ALCOHOL.  249 

ed  by  effervescence,  when  the  pressure 
of  the  cork  is  removed. 

Q.  Why  does  fresh  SPRING  WATER  SPARKLE, 
when  poured  from  one  vessel  to  another  ? 

A.  Because  fresh  spring-  and  pump 
water  contain  carbonic  acid  ;  and  it  is 
the  presence  of  this  gas  which  makes 
the  water  sparkle. 

Much  of  the  froth  and  bubbling  of  ale,  beer,  WATER, 
&c.,  when  they  are  "  poured  high,"  is  due  to  simple  me- 
chanical action. 

Q.  What  is  the  FERMENTATION  of  BEER  and 
WINE  1 

A.  The  escape  of  carbonic  acid,  pro- 
duced by  the  change  of  sugar  into  alco- 
hol. 

Q.       What  is  AL'COHOL  ? 

A.  The  spirit  of  beer  and  wine, 
obtained  by  fermentation. 

Q.       Of  what  ELEMENTS  is  AL'COHOL  composed  ? 

A.     Of  carbon,  oxygen,  and  hydrogen. 

Of  AL'COHOL,  4  parts  are  carbon,  2  oxygen,  and  6  hydrogen. 

Q.       What  are  the  ELEMENTS  of  grape  SUGAR  ? 

A.  Carbon,  oxygen,  and  hydrogen, 
all  in  equal  proportions. 

Q.       What   CHANGES   does  SUGAR  undergo  by 

FERMENTATION  ? 

A.  It  is  first  decomposed,  and  then 
its  elements  re-unite  in  different  propor- 
tions, producing  alcohol,  carbonic 
and  water. 

11* 


250  CARBONIC    ACID    GAS. 

Of  SUGAR,  one  portion  is  alcohol ;  and  another  carbonic 
acid ;  as  may  be  seen  by  the  following  table. 

Garb.    0x7.    Hyd. 

Every  atom  of  anhydrous  sugar  contains    12    12    12 


Two  atoms  of  alcohol  contain  8      4    12 

Four  atoms  of  carbonic  acid  contain  480 


12    12    12 

N.  B.     "  Anhydrous  sugar"  is  sugar  dried  at  300°. 

Q .  Ho w  does  s  UG  AR  form  AL' c  OH OL  by  fermen- 
tation ? 

A.  Two-thirds  of  its  carbon  and  one- 
ifhird  of  its  oxygen  re-unite  with  the 
Ihydrogen^  and  generate  alcohol. 

Q.  How  does  SUGAR  form  CARBONIC  ACID  by 
fermentation  ? 

A.  The  remaining  one-third  of  its 
•  carbon  and  two-thirds  of  its  oxygen  re- 
unite, arid  generate  carbonic  acid. 

Q.  What  BECOMES  of  the  AL'COHOL  which  is 
thus  generated  by  fermentation  ? 

A.  It  mixes  with  the  water,  and 
forms  the  intoxicating  part  of  beer  and 
wine. 

Q.  What  becomes  of  the  CARBONIC  ACID,  which 
is  generated  by  fermentation  ? 

A.     It  makes  its  escape  into  the  air. 

Q.       Why  is  BARLEY  MALTED  ? 

A.  Because  germination  is  produced 
by  the  artificial  heat;  and  in  germina- 
tion, the  starch  of  the  grain  is  converted 
into  sugar. 


BARLEY — YEAST.  251 

Q.      How  is  barley  malted  ? 

A.  It  is  moistened  with  water}  and 
heaped  up  ;  by  which  means,  great  heat 
is  produced,  which  makes  the  b&rley 
sprout. 

(See  "  spontaneous  combustion.") 

Q.  Why  is  not  the  BARLEY  suffered  to  GROW 
as  well  as  SPROUT  ? 

A.  Because  plants  in  the  germ  con- 
tain more  sugar  than  in  any  other  state : 
as  soon  as  the  germ  puts  forth  shoots,  the 
sugar  of  the  plant  is  consumed,  to  sup- 
port the  shoot. 

Q.  HOW  IS  BARLEY  PREVENTED  from  SHOOT- 
ING in  the  process  of  MALTING? 

A.  It  is  put  into  a  kiln,  as  soon  as  it 
sprouts  ;  and  the  heat  of  the  kiln  checks 
or  destroys  the  young  shoot. 

Q.       What  is  YEAST  ? 

A.  The  foam  of  beer  (or  of  some 
similar  liquor)  produced  by  fermentation. 

Q.       Why  is  YEAST  used  in  BREWING  ? 

A.  Because  it  consists  of  a  substance 
called  glu'ten,  undergoing  putrefaction ; 
in  which  state  it  possesses  the  peculiar 
property  of  exciting  fermentation. 

If  the  gluten  were  not  in  a  putrefying  state,  it  could 
not  produce  fermentation. 

Q.       What  is  gluten  ? 

A.     A  tough,  elastic  substance,  com- 


252  CARBONIC    ACID   GAS. 

posed  of  carbon,  oxygen,  hydrogen,  and 
nitrogen. 

Q.       Does  MALT  contain  gluten  ? 

A.  Yes.  The  infusion  of  malt,  called 
"  sweet- wort"  contains  an  abundance  of 
glu'ten ;  and  the  yeast  (which  converts 
its  sugar  into  alcohol]  converts  this  glu'- 
ten into  yeast. 

Q.  Why  is  YEAST  needful  in  order  to  make 
malt  into  BEER  ? 

A.  Because  the  presence  of  a  putre- 
fying body  containing  nitrogen  is  essen- 
tial, in  order  to  convert  sugar  into  al- 
cohol. 

Q.  What  EFFECT  has  yeast  upon  the  SWEET- 
WORT? 

A.  It  causes  the  SUGAR  to  be  con- 
verted into  alcohol  and  carbonic  acid; 
and  its  GLUTEN  into  yeast. 

Q.  What  change  is  produced  in  gluten  by  PU- 
TREFACTION ? 

A.  Its  elements  are  loosened  from 
their  former  conditions  of  combination, 
and  re-arranged  (with  the  addition  Af 
oxygen  from  the  air)  into  a  new  series. 

Q.  What  is  the  DIFFERENCE  between  FERMEN- 
TATION and  PUTREFACTION  ? 

A.  FERMENTATION  is  a  change  ef- 
fected in  the  elements  of  a  body  com- 
posed of  carbon,  oxygen,  and  hydrogen, 


PUTREFACTION.  253 


without  nitrogen.  PUTREFACTION  is  a 
change  effected  in  the  elements  of  a 
body  composed  of  carbon,  oxygen,  hy- 
drogen, and  nitrogen. 

Q.  What  NEW  COMPOUNDS  are  produced  by 
the  change  called  FERMENTATION  ? 

A.  Alcohol  and  carbonic  acid. — The 
alcohol  is  still  further  changed  (unless 
the  process  be  checked)  injp  acetic  acid 
or  vinegar. 

Q.  What  new  compounds  are  produced  by  the 
change  called  PUTREFACTION  ? 

A.  The  carbon,  oxygen,  hydrogen, 
and  nitrogen,  of  the  original  substance 
(being  separated  by  decomposition)  re- 
unite in  the  following  manner.  1.  Carbon 
and  oxygen  unite  to  form  carbonic  acid. 
2.  Oxygen  and  hydrogen  unite  to  form 
water.  3.  Hydrogen  and  nitrogen  unite 
to  form  ammonia. 

Hartshorn  is  a  solution  of  ammonia  in  water. 
N.  B.  When  bodies  containing  sulphur  and  phosphorus 
pntrefy,  the  sulphur  and  phosphorus  unite  with  hydrogen, 
and  form  sulphuretted  and  phosphurctted  hydrogen  gases. 

Q.  What  BECOMES  of  these  several  products  of 
putrefaction  ? 

A.  They  are  all  elastic  bodies,  and 
escape  into  the  air. 

N.  B.  Water  is  elastic  and  gaseous  when  in  the  condi- 
tion of  vapor. 

Q.  What  is  the  cause  of  the  OFFENSIVE  SMELL 
which  issues  from  putrefying  bodies  ? 


254  CARBONIC    ACID    GAS. 

A.  The  evolution  of  ammonia,  or  of 
sulphuretted  and  phosp/iuretted  hydrogen 
gases ;  all  of  which  have  pungent  and 
offensive  odors. 

Q.  Why  do  boiled  EGGS  DISCOLOR  a  SILVER 
SPOON  ? 

A.  Because  they  contain  a  small 
portion  of  sulphur,  which  unites  with  the 
silver  (for  which  it  has  a  great  affinity) 
and  tarnishes  it. 

Both  the  white  and  yolk  contain  sulphur — the  latter 
more  abundantly. 

Q.  What  causes  the  offensive  smell  of  STALE 
hard  boiled  EGGS? 

A.  The  hydrogen  of  the  egg  combin- 
ing with  the  sulphur  and  phosphorus, 
form  sulphuretted  and  pfiosphurctted  hy- 
drogen; both  of  which  gases  have  an 
offensive  odor. 

Of  an  egg  55  parts  are  carbon,  16  nitrogen,  7  hydrogen, 
and  the  remaining  22  are  oxygen,  phosphorus,  and  sul- 
phur. 

Q.  Why  is  it  NOT  needful  to  put  YEAST  into 
GRAPE  juice,  in  order  to  produce  fermentation,  ? 

A.  Because  grape  juice  contains  a 
sufficient  quantity  of  a  nitrogenized 
substance  (like  yeast)  to  produce  fermen- 
tation. 

Nitrogenized,  i.  e.,  containing  nitrogen. 

Q.  Why  do  NOT  GRAPES  ferment,  while  they 
hang  on  the  VINE  ? 


FERMENTATION.  255 

A.  Because  the  water  of  the  juice 
evaporates  through  the  skin,  and  allows 
the  grapes  to  shrivel  and  dry  up,  after 
they  are  ripe. 

Fermentation  cannot  occur  unless  the  sugar  be  dissolved 
in  a  sufficient  quantity  of  water. 

Q.  What  is  the  FROTH  or  SCUM  of  fermented 
LIQUORS  ? 

A.  Putrefying-  glutinous  substances 
(of  a  nature  similar  to  yeast),  which  rise 
to  the  surface  from  their  lightness. 

Q.  Why  is  BEER  FLAT  if  the  cask  be  left  open 
too  long  ? 

A.  Because  too  much  of  the  carbonic 
acid  gas  (produced  by  fermentation)  is 
suffered  to  escape. 

Q.  Why  are  BEER  and  PORTER  made  STALE  by 
being  exposed  to  the  AIR  ? 

A.  Because  too  much  of  the  carbonic 
acid  gas  (produced  by  fermentation)  is 
suffered  to  escape. 

Q.       Why  does  BEER  turnFLAT  if  the  VENT  PEG 

be  left  out  of  the  tub? 

A.  Because  the  carbonic  acid  gas  es- 
capes through  the.  vent  hole. 

Q.  Why  will  NOT  beer  RUN  OUT  of  the  tub  till 
the  VENT  PEG  is  taken  out  ? 

A.  Because  the  upward  pressure  of 
the  external  air  (admitted  through  the 
tap)  holds  the  liquor  back — not  being 


256  CARBONIC    ACID    GAS. 

counterbalanced  by  any  pressure  of  air 
on  the  surface  of  the  liquid. 

The  upward  pressure  of  air  is  illustrated  by  the  follow- 
ing simple  experiment: — Fill  a  wine  glass  with  water; 
cover  the  top  of  the  glass  with  a  piece  of  writing  paper 
turn  the  glass  upside  down,  and  the  water  will  not  run 
out.  The  paper  is  used  merely  to  give  the  air  a  medium 
sufficiently  dense  to  act  against. 

Q.  Why  does  the  BEER  RUN  FREELY,  imme- 
diately the  VENT  PEG  is  taken  out  ? 

A.  Because  air  rushes  immediately 
through  the  vent  hole  at  the  top  of  the  tub, 
to  counterbalance  the  air  admitted  by 
the  tap ;  in  consequence  of  which  the 
liquid  escapes  by  its  own  downward 
pressure. 

Q.  Why  does  liquor  flow  reluctantly  out  of  a, 
BOTTLE  held  upside  down  ? 

A.  Because  the  upward  pressure  of 
the  air  prevents  the  liquor  from  flowing" 
out. 

Q.  Why  should  a  bottle  be  held  OBLIQUELY  in 
order  to  be  emptied  of  its  liquor  ? 

A.  Because  air  will  then  flow  into 
the  bottle,  and  help  the  liquor  out,  by 
counterbalancing  the  upward  pressure. 

Q.  Why  does  wine  (poured  from  a  bottle 
QUICKLY)  SPIRT  about,  without  going  into  the 
decanter  ? 

A.  Because  it  fills  the  top  of  the  de- 
canter (like  a  cork),  and  leaves  no  room 


YEAST — FERMENTATION.  257 

for  the  air  inside  to  escape ;  the  decanter, 
therefore,  (being-  full  of  air]  refuses  to 
admit  the  wine. 

Q.  Why  does  the  EFFERVESCENCE  of  soda  water 
a?id  ginger  beer  so  soon  go  off? 

A.  Because  the  carbonic  acid,  (which 
produced  the  effervescence)  very  rapidly 
escapes  into  the  air. 

Q.       Why  is  BOILED  WATER  FLAT  and  insipid  ? 

A.  Because  the  whole  of  the  carbonic 
acid  is  expelled  by  boiling1,  and  escapes 
into  the  air. 

Q.       Why  does  YEAST  make  BREAD  LIGHT  ? 

A.  Because  it  produces  a  species  of 
fermentation  on  the  starch  and  glu'ten 
of  flour,  as  it  does  in  the  sug*ar  of  malt. 

Q.  How  does  FERMENTATION  make  the  DOUGH 
RISE  ? 

A.  During*  fermentation,  carbonic  acid 
gas  is  evolved ;  but  the  sticky  texture  of 
the  dough  will  not  allow  it  to  escape; 
so  it  forces  up  little  bladders  all  over  the 
doug-h. 

Q.       Why  is  DOUGH  placed  BEFORE  the  FIRE  ? 

A.  1st — Because  the  heat  of  the  fire 
increases  the  fermentation ;  and 

2dly — It  expands  the  gas.  confined  in 
the  little  bladders ;  in  consequence  of 
which,  the  bladders  are  enlarged,  and 


258  CARBONIC    ACID    GAS. 

the  dough  becomes  lighter  and  more  po- 
rous. 

Q.  Why  is  BREAD  HEAVY,  if  the  dough  be  re- 
moved from  the  fire? 

A.  Because  the  dough  gets  cold,  and 
then  the  air  in  the  bladders  condenses — 
the  paste  falls — and  the  bread  becomes 
close  and  heavy. 

Q.       What  causes  the  HEAT  of  FIRE  ? 

A.  The  carbon  of  fuel  (when  heated) 
combines  with  the  oxygen  of  the  air,  and 
produces  carbonic  acid  gas :  Again,  the 
hydrogen  of  the  fuel  combining  with 
other  portions  of  oxygen,  condenses  into 
water ;  by  which  chemical  actions  heat 
is  evolved. 

Q.       What  causes  the  HEAT  of  our  own  BODY  ? 

A.  The  carbon  of  our  blood  combines 
with  the  oxygen  of  the  air  inhaled^  and 
produces  carbonic  acid  gas ;  which 
evolves  heat  in  a  way  similar  to  burn- 
ing fuel. 

Q.  WHience  does  the  HEAT  of  a  DUNGHILL 
arise  ? 

A.  As  the  straw,  &c.,  of  the  dunghill 
decays,  it  undergoes  fermentation,  which 
produces  carbonic  acid  gas  ;  and  heat  is 
evolved  by  a  species  of  combustion,  (as 
in  the  two  former  cases.) 


LIME WATER.  259 

Q.  How  does  the  formation  of  CARBONIC  ACID 
(in  all  these  cases)  produce  HEAT  ? 

A.  Carbonic  add  has  less  power  of 
holding  latent  heat  than  carbon  and  oxy- 
gen have :  When,  therefore,  these  ele- 
ments are  changed  into  carbonic  acid, 
latent  heat  is  given  off,  arid  made  sensible.' 

Q.  Why  do  persons  throw  LIME  into  BINS  and 
SEWERS,  to  PREVENT  their  offensive  SMELL,  in  sum- 
mer time  ? 

A.  Because  they  contain  large  quan- 
tities of  carbonic  acid  gas,  which  readily 
combines  with  lime  ;  and  producing  "  car- 
bonate of  lime"  neutralizes  the  offensive 
gases. 

Q.  Why  should  WATER  (used  for  washing]  be 
exposed  to  the  air  ? 

A.  Because  it  is  made  more  soft  by 
exposure  to  the  air. 

Most  spring  water  holds  lime  in  solution  as  a  bicarbon- 
ate, in  consequence  of  the  presence  of  abundant  carbonic 
acid.  Carbonic  acid  escapes  by  exposure  to  air — and  the 
lime  is,  consequently,  deposited  as  a  carbonate. 

Q.  Why  is  hard  WATER  made  more  SOFT  by 
exposure  to  air  ? 

A.  1st — Because  the  mineral  salts 
(which  cause  its  hardness)  subside  :  and 

2dly — Because  the  carbonic  acid  of 
the  water  makes  its  escape  into  the  air. 

Q.      How  is  the  carbonic   acid  of  water 
duced  ? 


260  CARBONIC    ACID    GAS, 

A.  From  the  presence  of  lime,  which 
is  frequently  held  in  solution  by  hard 
water :  When  the  carbonic  acid  escapes 
by  exposure  to  the  air,  the  lime  is  depos- 
ited as  a  carbonate. 

Q.  Why  is  HARD  WATER  more  agreeable  to 
DRINK  than  soft  water  ? 

A.  Chiefly-  because  it  contains  car- 
bonic acid. 

Q.  Why  is  water  FRESH  from  the  pump  more 
SPARKLING,  than  after  it  has  been  drawn  some  time  ? 

A.  Because  water  fresh  from  the 
pump  contains  carbonic  acid,  which  soon 
escapes  into  the  air,  and  leaves  the  wa- 
ter flat  and  stale. 

Q.  Why  is  QUICK-LIME  formed  by  burning 
chalk  and  marl  in  a  KILN  ? 

A.  Because  the  carbonic  acid  (which 
rendered  it  mild)  is  driven  off  by  the 
heat  of  the  kiln :  and  the  lime  becomes 
quick  or  caustic. 

Q.       What  is  MORTAR  ? 
A.     Quick-lime  mixed  with  sand  and 
water. 

Q.  Wherein  does  LIME-STONE  differ  in  appear- 
ance from  quick-lime  ? 

A.  LIME-STONE  is  a  hard,  rocky  sub- 
stance ;  but  QUICK-LIME  a  loose  powder. 

Q.  Why  does  MORTAR  become  HARD  after  a  few 
days  ? 


MORTAR — CHOKE-DAMP.  261 

A.  Because  the  lime  re-imbibes  from 
the  air  the  carbonic  acid  which  had 
been  expelled  by  fire  ;  and  the  loose  pow- 
der again  becomes  as  hard  as  the  origi- 
nal lime-stone. 

§       Explain  in  what  way  MORTAR  is  adhesive. 
When  the  carbonic  acid  is  expel- 
he  hard  lime-stone  is  converted  into 
a  loose  powder •,  which  (being*  mixed  with 
sand    and    water)  becomes  a  soft   and 
sticky  plaster  ;  but  as  soon  as  it  is  placed 
between  bricks,  it  imbibes  carbonic  acid 
again,  and  hardens  into  lime-stone. 


CARBURETTED  HYDROGEN  GAS. 

CHAPTER  XXII. 

Q.       What  is  CHOKE-DAMP  ? 

A.  Carbonic  acid  gas  accumulated 
at  the  bottom  of  wells  and  pits.  It  is 
called  CHOKE  damp,  because  it  chokes  (or 
suffocates)  every  animal  that  attempts  to 
inhale  it.  (Seep.  238;) 

It  suffocates  without  getting  into  the  lungs,  by  closing 
the  outer  orifice  spasmodically. 

Q.       What  is  marsh-gas  or  FIRE-DAMP  ? 

A.     Carburetted  hydrogen  gas   accu- 


262       CARBURETTED    HYDROGEN    GAS. 

mulated  on  marshes,  in  stagnant  waters, 
and  coal-pits  ;  it  is  frequently  called 
"  inflammable  air." 

Q.       What  is  CARBURETTED  HYDROGEN  GAS  ? 

A.      Carbon  combined  with  hydrogen. 

Q.  How  may  CARBURETTED  HYDROGEN  GAS 
be  PROCURED  on  marshes? 

A.  By  stirring  the  mud  at  the  bottom 
of  any  stagnant  pool,  and  collecting-  the 
gas  (as  it  escapes  upwards)  in  an  in- 
verted glass  vessel. 

Q.       What  is  COAL  GAS  ? 

A.  Carburetted  hydrogen  extracted 
from  coals  by  the  heat  ofjire. 

Q.  Why  is  carburetted  hydrogen  gas  called 
FIRE-DAMP  or  inflammable  air  ? 

A.  Because  it  very  readily  catclies 
fire  and  explodes,  when  a  light  is  intro- 
duced to  it. 

Provided  atmospheric  air  be  present. 
Q.       Why  is  carburetted  hydrogen  gas  frequent- 
ly called  MARSH-GAS  ? 

A.  Because  it  is  generated  in  mea- 
dows and  marshes  from  putrefying  vege- 
table substances. 

See  ignis  fatuus,  p,  266. 

Q.  What  gas  is  evolved  by  the  WICK  of  a 
turning  CANDLE  ? 

A.  Carburetted  hydrogen  gas :  The 
carbon  and  hydrogen  of  the  tallow  com- 


DAVY'S  SAFETY  LAMP.  263 

bine  into  a  gas  from  the  heat  of  the 
flame;  and  this  gas  is  called  carbureUed 
hydrogen  or  inflammable  air. 

Q.  Why  do  COAL-MINES  so  frequently  EX- 
PLODE ? 

A.  Because  the  CMrburetted  hydrogen 
gas  (which  is  generated  in  these  mines 
by  the  coals)  explodes,  when  a  light  is 
incautiously  introduced. 

Q.  How  -can  miners  SEE  in  the  coal-pits  if 
they  may  never  introduce  a  LIGHT  ? 

A.  Sir  Humphrey  Davy  invented  a 
lantern  for  the  use  of  miners,  called  "  the 
Safety  Lamp,"  which  may  be  used  with- 
out danger. 

Q.       Who  was  SIR  HUMPHREY  DAVY? 

A.  A  very  clever  chemist,  born  in 
Cornwall,  1778,  and  died  in  1829. 

Q.       What  kind  of  thing  is  the  SAFETY-LAMP  ? 

A.  A  kind  of  lantern,  covered  with  a 
fine  gauze  wire,  instead  of  glass  or  horn. 

Q.  How  does  this  fine  GAUZE  WIRE  prevent  an 
EXPLOSION  in  the  coal-mine  ? 

A.  By  preventing  the  flame  of  the 
lamp  from  communicating  with  the  in- 
flammable gas  of  the  mine. 

N.  B.    The  interstices  of  the  gauze  wire  must  not  ex- 
ceed the  7th  of  an  inch  in  diameter. 

Q.  Why  will  not  FLAME  PASS  THROUGH  very 
fine  wire  GAUZE  ? 


264       CARBURETTED    HYDROGEN    GAS. 

A.  Because  the  metal  wire  is  a  very 
rapid  conductor  of  heat ;  and  when  the 
flame  (of  gas  burning*  in  the  lamp)  reach- 
es the  wire  gauze,  so  much  heat  is  con- 
ducted away  by  the  wire,  that  the  flame  is 
extinguished. 

Q.  Does  the  gas  of  the  COAL-PIT  get  THROUGH 
the  wire  gauze  INTO  the  LANTERN  ? 

A.  Yes ;  and  the  inflammable  gas 
ignites,  and  burns  inside  the  lamp :  As 
soon  as  this  is  the  case,  t/w  miner  is  in 
danger,  and  should  withdraw. 

Q. .  Why  is  the  miner  in  DANGER  if  the  gas  ig- 
nites and  burns  in  the  INSIDE  of  the  safety  lamp  ? 

A.  Because  the  heat  of  the  burning 
gas  will  soon  destroy  the  wire  gauze ;  and 
then  the  flame  (being  free)  will  set  fire 
to  the  mine. 

N.  B.  When  the  carburetted  hydrogen  gas  takes  fire 
from  the  miner's  candle,  the  miner  sometimes  perishes  in 
the  blastof  the  flame,  and  sometimes  suffers  suffocation  from 
the  carbonic  acid  which  is  thus  produced. 


PHOSPHORUS.  265 

PHOSPHURETTED   HYDROGEN 
G-AS. 

CHAPTER   XXIII. 

Q.  From  what  do  the,  very  OFFENSIVE  EFFLU- 
VIA of  CHURCH-YARDS  arise  ? 

A.  From  a  gas  called  PHOSPHURET- 
TED HYDROGEN  ;  which  is  phosphorus 
combined  with  hydrogen  gas. 

Q.       What  is  PHOSPHORUS? 

A.  A  pale  amber-colored  substance, 
resembling*  wax  in  appearance.  The 
word  is  derived  from  two  Greek  words, 
which  mean  "  to  produce  or  carry  light" 

(00)£-0£J9«V). 

Q.         HOW  is  PHOSPHORUS    OBTAINED  ? 

A.  By  heating-  bones  to  a  white 
heat ;  by  which  means,  the  animal  mat- 
ter arid  charcoal  are  consumed,  and  a 
substance  called  "phosphate  of  lime"  is 
left  behind. 

Q.       What  is  the  PHOSPHATE  OF  LIME  ? 

A.  Phosphorus  united  to  oxyg*en  and 
lime ;  when  sulphuric  acid  is  added,  and 
the  mixture  heated,  the  lime  is  attracted 
to  the  acid,  and  pure  phosphorus  remains. 

If  powdered  charcoal  be  added,  phosphorus  may  be 
procured  by  distillation. 

Q.  Of  what  is  the  ignitible  part  of  LUCIFER 
MATCHES  made  ? 

12 


266      PHOSPHURETTED  HYDROGEN  GAS. 

A.  Of  phosphorus  :  and  above  250 
thousand  Ibs.  are  used  every  year  in 
London  alone,  merely  for  the  manufac- 
ture of  lucifer  matches. 

Q.  Why  does  a  PUTREFYING  dead  BODY 
SMELL  so  offensively  ? 

A.  Because  phosphuretted  hydrogen 
gas  always  rises  from  putrefying*  animal 
substances. 

The  escape  of  ammonia  and  sulphuretted  hydrogen  con- 
tributes also  to  this  offensive  effluvia. 

Q.  What  is  the  cause  of  the  IGNIS  FATUUS, 
Jack  0' Lantern,  or  Will  o'the  Wisp? 

A.  This  luminous  appearance  (which 
haunts  meadows,  bogs,  and  marshes) 
arises  from  the  gas  of  putrefying  animal 
and  vegetable  substances  ;  especially  from 
decaying*  fish. 

Q.  What  gases  arise  from  these  PUTREFYING 
substances  ? 

A.  Phosphuretted  hydrogen  from  pu- 
trefying* animal  substances :  and 

Carburetted  hydrogen,  from  decaying* 
vegetable  matters.  (See  p.  262.) 

Q.  How  is  the  gas  of  the  ignis  fatuus  IGNITED 
on  bogs  and  meadows  ? 

A.  Impure  phosphuretted  hydrog*en 
bursts  spontaneously  into  flame,  whenever 
it  mixes  with  air  or  pure  oxygen  g*as. 

Pure  phosphuretted  hydrogen  will  not  ignite  spontane- 
ously— this  spontaneous  ignition  is  due  to  the  presence  c* 


IGNIS    FATUUS.  267 

a  small  quantity  of  the  vapor  of  an  exceedingly  volatile  li- 
quid-compound of  phosphorus  with  hydrogen,  which  is 
occasionally  produced  with  the  gas  itself. 

If  phosphorus  be  boiled  with  milk  of  lime,  and  the  beak 
of  the  retort  be  placed  under  water,  bubbles  of  phosphuret- 
ted  hydrogen  will  rise  successively  through  the  water,  and 
(on  reaching  the  surface)  burst  into  flame.  ^ 

Q.  Why  does  an  ignis  faluus  or  Will  oHhe 
Wisp  FLY  from  us  when  we  RUN  to  MEET  it  ? 

A.  Because  we  produce  a  current  of 
air  in  front  of  ourselves,  (when  we  run 
towards  the  ignis  fatuus)  which  drives  the 
light  gas  forwards. 

Q.  Why  does  an  ignis  fatuus  run  AFTEII  us 
when  we  FLEE /raw  it  in  a  fright  ? 

A.  Because  we  produce  a  current  of 
air  in  the  way  we  run,  which  attracts  the 
light  gas  in  the  same  course;  drawing  it 
after  us  as  we  run  away  from  it. 

Q.  Is  not  a  kind  of  Jack  o*  Lantern  sometimes 
produced  by  an  INSECT  ? 

A.  Yes ;  swarms  of  luminous  insects 
sometimes  pass  over  a  meadow,  and 
produce  an  appearance  similar  to  the 
ignis  fatuus. 

Q.  May  not  many  GHOST  stories  have  arisen 
from  some  ignis  faluus  lurking  about  church-yards  ? 

A.  Perhaps  all  the  ghost  stories 
(which  deserve  any  credit  at  all)  have 
arisen  from  the  ignited  gas  of  church- 
yards, lurking  about  the  tombs ;  to  which 
fear  has  added  its  own  creations. 


268  WIND. 

WIND. 

CHAPTER  XXIV. 

Q.       What  is  WIND  ? 

A.     Wind  is  air  in  motion. 

Q.  What  PUTS  the  air  in  motion^  so  as  to  pro- 
duce WIND? 

A.  The  principal  causes  are  the 
variations  of  heat  and  cold,  produced  by 
the  succession  of  day  and  night j  and  of 
the  four  seasons. 

Q.       What  effect  has  HEAT  upon  the  air  ? 

A.  Heat  rarejies  the  air  and  causes  it 
to  expand. 

Q.  How  do  you  KNOW  that  heat  causes  the  air 
to  EXPAND  ? 

A.  Thus,  if  a  bladder  half  full  of  air 
(tied  tight  round  the  neck)  be  laid  before 
a  j^re,  the  air  will  expand  by  the  heat, 
and  fill  the  bladder. 

Q.       What   EFFECT  is  produced  upon  air   by 

RAREFACTION  ? 

A.  It  is  made  lighter  and  ascends 
through  colder  strata ;  as  a  cork  (put  at 
the  bottom  of  a  basin  of  water)  rises  to 
the  surface. 

Q.        Prove  that  rarefied  air  ASCENDS. 
A.     When  a  boy  sets  fire  to  the  cotton 
or  sponge  of  his  balloon,  the  flame  heats 


AIR.  269 

the  air  ;  which  becomes  so  light,  that  it 
ascends,  and  carries  the  balloon  with  it. 
Q.       What  effect  is  produced  upon  AIR  by  COLD  ? 

A.  It  is  condensed,  or  squeezed  into 
a  smaller  compass  :  in  consequence  of 
which,  it  becomes  heavier,  and  descends 
towards  the  ground. 

Q.      Prove  that  air  is  condensed  by  COLD. 

A.  Lay  a  bladder  half  full  of  air 
before  a  fire,  till  it  has  become  fully 
inflated;  if  it  be  now  removed  from  the 
fire,  the  bladder  will  collapse  again,  be- 
cause the  air  condenses  into  its  former 
bulk. 

Q.  What  is  meant  by  the  bladder  "  COLLAPS- 
ING ?" 

A.  The  skin  becoming1  wrinkled, 
shrivelled,  and  flabby ;  because  there  is 
not  sufficient  air  inside  to  Jill  it. 

Q.  How  do  you  KNOW  that  CONDENSED  air 
will  DESCEND? 

A.  Because  afire  balloon  falls  to  the 
earth,  so  soon  as  the  spirit  in  the  cotton 
is  burnt  out,  and  the  air  of  the  balloon 
has  become  cold  again. 

Q.  Does  the  SUN  HEAT  the  AIR  as  it  does  the 
EARTH  ? 

A.  No ;  the  air  is  not  heated  by  the 
rays  of  the  sun  ;  because  air  (like  water) 
is  a  very  bad  conductor. 


270  WIND. 

Q.      How  is  the  AIR  HEATED  1 

A.  By  convection,  thus  : — The  sun 
heats  the  earth,  and  the  earth  heats  the 
air  resting  upon  it ;  the  air  thus  heated 
rises,  and  is  succeeded  by  other  air,  which 
is  heated  in  a  similar  way  ;  till  the  whole 
volume  is  warmed  by  "  convective  cur- 
rents." 

Q.  What  is  meant  by  "CONVECTIVE  CURRENTS" 
of  hot  air  ? 

A.  Streams  of  air  heated  by  the 
earth,  which  rise  upwards,  and  carry 
heat  with  them.  (See  p.  226.) 

Q.  Is  the  air  in  a  ROOM  in  perpetual  motion  as 
the  air  ABROAD  is  ? 

A.  Yes;  there  are  always  two  cur- 
rents of  air  in  the  room  we  occupy;  one 
of  hot  air  flowing-  out  of  the  room,  and 
another  of  cold  air  flowing-  into  the  room. 

Q.  How  do  you  KNOW  that  there  are  these  TWO 
currents  of  air  in  every  occupied  ROOM  1 

A.  If  I  hold  a  lighted  candle  near 
the  crevice  at  the  top  of  the  door,  the 
flame  will  be  blown  outward  (towards 
the  hall] ;  but  if  I  hold  the  candle  at  the 
bottom  of  the  door,  the  flame  will  be 
blown  inwards  (into  the  room). 

N.  B.  This  is  not  the  case  if  a,  fire  be  in  the  room.  When 
a  fire  is  lighted,  an  inward  current  is  drawn  through  all 
the  crevices. 

Q.       Why  would  the  flame  be  blown  OUTWARDS 


CANDLE  FLAME.  271 

(towards  the  HALL),  if  a  candle  be  held  at  the  TOP  of 
the  door  ? 

A.  Because  the  air  of  the  room  being* 
heated,  &c.,  ascends  ;  and  (floating  about 
the  upper  part  of  the  room)  some  of  it 
escapes  through  the  crevice  at  the  top  of 
the  door,  producing*  a  current  of  air  out- 
wards (into  the  hall), 

Q.  Why  would  the  flame  be  blown  INWARDS 
(into  the  ROOM),  if  the  ca?idle  be  held  at  the  BOTTOM 
of  the  door  ? 

A.  Because  a  partial  vacuum  is  made 
at  the  bottom  of  the  room,  as  soon  as  the 
warm  air  of  the  room  has  ascended  to 
the  ceiling1,  or  made  its  escape  from  the 
room :  and  cold  air  from  the  hall  rushes 
under  the  door,  to  supply  the  void. 

Q.  What  is  meant  by  a  "partial  VACUUM  be- 
ing made  at  the  BOTTOM  of  the  ROOM  ?" 

A.  A  vacuum  means  a  place  from 
which  the  air  has  been  taken:  and  a 
"  partial  vacuum  "  means  a  place  from 
which  a  part  of  the  air  has  been  taken 
away.  Thus,  when  the  air  on  the  floor 
ascends  to  the  ceiling-,  a  partial  vacuum 
is  made  on  the  floor. 

Q.      And  how  is  the  VACUUM  filled  UP  again  ? 

A.  It  is  filled  up  by  colder  air,  which 
rushes  (under  the  cfoor,  and  through  the 
window  crevices)  into  the  room. 


272  WIND. 

Q.       Give  me  an  ILLUSTRATION. 

A.  If  I  dip  a  pail  into  a  pond  and 
fill  it  with  water,  a  hole  (or  vacuum)  is 
made  in  the  pond  as  big  as  the  pail ;  but 
the  moment  I  draw  the  pail  out,  the  hole 
is  filled  up  by  the  water  around. 

Q.       Show  how  this  illustration  APPLIES. 

A.  The  heated  air,  which  ascends 
from  the  bottom  of  a  room,  is  as  much 
taken  away  as  the  water  in  the  pail ; 
and  (as  the  void  was  instantly  supplied 
by  other  water  in  the  pond)  so  the  void  of 
air  is  supplied  by  the  air  around. 

Q.       What  is  the  CAUSE  of  WIND  ? 

A.  The  sun  heats  the  earth,  and  the 
earth  heats  the  air  resting1  upon  it ;  as 
the  warm  air  ascends,  the  void  is  filled 
up  by  a  rush  of  cold  air  to  the  place ;  and 
this  rush  of  air  we  call  WIND. 

Q.      Does  the  WIND  ALWAYS  blow  ? 

A.  Yes  ;  there  is  always  some  motion 
in  the  air ;  but  the  violence  of  the  motion 
is  perpetually  varying1. 

Q.  Does  the  rotation  of  the  earth  upon  its  axis 
affect  the  motion  of  the  air  ? 

A.  Yes,  in  two  ways.  1st — As  the 
earth  moves  round  its  axis,  the  thin 
moveable  air  is  left  somewhat  behind; 
and,  therefore,  seems  (to  a  stationary" 


VERTICAL   RAYS.  273 

object)  to  be  blowing-  in  the  opposite  di- 
rection to  the  earth's  motion  :  and 

2dly — As  the  earth  revolves,  different 
portions  of  its  surface  are  continually 
passing-  under  the  vertical  rays  of  the 
sun. 

Q.  When  are  the  rays  of  the  sun  called  "  VER- 
TICAL RAYS  ?" 

A.  When  the  sun  is  in  a  direct  line 
above  any  place,  his  rays  are  said  to  be 
"  vertical  "  to  that  place. 

Q.  Illustrate  the  manner  in  which  the  earth's 
surface  passes  under  the  vertical  sun. 

A.  Suppose  the  brass  meridian  of  a 
globe  to  represent  the  vertical  rays  of 
the  sun ;  as  you  turn  the  g-lobe  round, 
different  parts  of  it  will  pass  under  the 
brass  rim,  in  constant  succession. 

Q.  Why  is  it  NOON-DAY  to  the  place  over  which 
the  SUN  is  VERTICAL  ? 

A.  Because  the  sun  is  half-way  be- 
tween rising*  and  setting-  to  that  place. 

Q.  Show  how  this  ROTATION  of  the  earth  affects 
the  AIR. 

A.  If  we  suppose  the  brass  meridian 
to  be  the  vertical  sun,  the  whole  column 
of  air  beneath  will  be  heated  by  the  noon- 
day rays ;  that  part  which  the  sun  has 
left,  will  become  gradually  colder  and 
colder ;  and  that  part  to  which  the  sun 
12* 


274  WIND. 

is   approaching,   will    grow    constantly 
warmer  and  ivarmer. 

Q.  Then  there  are  THRE£  qualities  of  air  about 
this  spot  ? 

A.  Yes ;  the  air  over  the  place,  which 
has  passed  the  meridian,  is  cooling;  the 
air  under  the  vertical  sun  is  the  hottest  ; 
and  the  air,  which  is  over  the  place  about 
to  pass  under  the  meridian,  is  increasing 
in  heat. 

See  fig.  on  next  page.  The  column  A  (which  the  sun 
has  passed)  is  cooling — B  is  under  the  vertical  sun ;  and 
-C  is  increasing  in  heat. 

Q.  How  does  this  VARIETY  in  the  HEAT  of  AIR 
produce  WIND  ? 

A.  The  air  always  seeks  to  preserve 
<an  equilibrium ;  so  cold  air  rushes  into 
the  void  made  by  the  ujncard  current  of 
<the  warm  air. 

Q.  Why  does  not  the  wind  ALWAYS  BLOW 
ONE  way,  following  the  direction  of  the  SUN  ? 

A.  Because  the  direction  of  the  wind 
is  subject  to  perpetual  interruptions  from 
hills ,  arid  valleys,  deserts,  seas,  &c. 

Q.  How  can  HILLS  and  MOUNTAINS  ALTER  the 
course  of  the  WIND  ? 

A.  Suppose  a  wind  (blowing-  from 
the  north)  comes  to  a  mountain ;  as  it 
cannot  pass  through  it,  it  must  either 
rush  back  again,  or  fly  off  at  one  side,  (as 
a  marble,  when  it  strikes  against  a  wall.) 


MOUNTAINS — OCEAN.  275 

Q.  Do  MOUNTAINS  affect  the  wind  in  any  OTHER 
way? 

A.  Yes ;  many  mountains  are  capped 
with  snow?,  and  the  warm  air  is  condensed, 
when  it  comes  in  contact  with  them  ;  but 
so  soon  as  the  temperature  of  the  wind  is 
changed,  its  direction  may  be  changed 
also.  (See  Fig.} 

THE   SUN. 


Suppose  ABC  to  be  three  columns  of  air.  A,  the  col- 
umn of  air  which  is  cooling  down  ;  B,  the  column  to  which 
the  sun  is  vertical;  and  C  the  column  which  is  to  be  heated 
next.  In  this  case  the  cold  air  of  A  will  rush  towards  B  C  ; 
because  the  air  of  B  and  C  is  hotter  than  A.  But  suppose 
now  C  to  be  a  snow-capped  mountain :  As  the  hot  air  of  B 
reaches  C,  it  is  chilled',  and  (being  now  colder  than  the  air 
behind)  it  rushes  back  again  towards  A,  instead  of  follow- 
ing the  sun. 

Q.  Hoio  can  the  OCEAN  affect  the  direction  of 
the  WIND  ? 

A.  When  the  ocean  rolls  beneath  the 
vertical  sun,  the  water  is  not  made  so  hot 
as  the  land;  in  consequence  of  which, 
the  general  direction  of  the  wind  is  di- 
rected from  tracts  of  ocean  towards  tracts 
of  land. 

Q.       Why  is  not  the  WATER  of  the  sea  made  so 


276  WIND. 

HOT,    b?/   the  vertical  sun,   as   the   surface  of  the 

LAND? 

A.  1st — Because  the  evaporation  of 
the  sea  is  greater  than  that  of  the  land : 

2dly — The  constant  motion  of  the 
water  prevents  the  increase  of  tempera- 
ture at  the  surface  :  and 

3dly — The  rays  of  the  sun  strike  into 
the  water  ;  in  consequence  of  which  the 
immediate  surface  is  much  less  affected. 

Q.  Why  does  the  EVAPORATION  of  the  sea  pre- 
vent its  surface  from  being  HEATED  by  the  vertical 
sun  ? 

A.  Because  its  heat  is  absorbed  in  the 
generation  of  vapor  and  carried  off  into 
the  air. 

Q.  Why  does  the  MOTION  of  the  sea  prevent  its 
surface  from  being  HEATED  by  the  vertical  sun  ?  . 

A.  Because  each  portion  rolls  away, 
as  soon  as  it  becomes  heated,  and  is 
succeeded  by  another ;  and  this  constant 
motion  prevents  the  surface  of  the  sea 
from  being*  more  heated  than  the  water 
below  the  surface. 

Q.       Do  CLOUDS  affect  the  WIND  ? 

A.  Yes.  As  passing1  clouds  screen 
the  direct  heat  of  the  sun  from  the  earth, 
they  diminish  the  rarefaction  of  the  air 
also  ;  and  this  is  another  cause  why  nei- 


TRADE    WINDS.  277 

ther  the  .strength  nor  direction  of  the 
wind  is  uniform. 

Q.  Would  the  wind  blow  regularly  from  east 
to  west,  if  these  OBSTRUCTIONS  were  REMOVED  ? 

A.     Without    doubt.      If  the   whole ' 
earth  were  covered  with  water  the  winds 
would  always  follow  the  sun,  and  blow 
uniformly  in  one  direction. 

Q.      Do  winds  EVER  blow  REGULARLY  ? 

A.  Yes :  in  those  parts  of  the  world, 
which  present  a  large  surface  of  water, 
as  in  the  Atlantic  and  Pacific  Oceans, 

Q.  What  are  the  winds,  which  blow  over  the 
ATLANTIC  and  PACIFIC  Oceans,  called  ? 

A.     They  are  called  "  Trade  Winds." 

Q.       Why  are  they  called  "  TRADE  WINDS/' 

A.  Because  they  are  very  convenient 
to  merchants,  who  have  to  cross  the 
ocean,  inasmuch  as  they  always  blow 
in  one  direction. 

Q.  In  what  DIRECTION  do  the  TRADE  WINDS 
blow  ? 

A.  That  in  the  northern  hemisphere 
blows  from  the  north-east;  that  in  the 
southern  hemisphere  from  the  south-east. 

Q.  Why  do  they  not  blow  from  the  FULL 
NORTH  and  SOUTH  ? 

A.  Because  currents  of  air  flowing 
from  the  poles,  give  them  an  easterly  di- 
rection. 


278  WIND. 

This  effect  is  due  in  some  measure  to  the  rotation  of  the 
earth  on  its  axis. 

Q.  What  is  the  cause  of  these  currents  of  air 
from  the  POLES  to  the  EQUATOR  ? 

A.  The  air  about  the  equator  con- 
stantly ascends,  in  consequence  of  being* 
rarefied  by  the  heat  of  the  sun  :  as  the 
hot  equatorial  air  ascends,  cold  air  from 
the  north  and  south  flows  towards  the 
equator,  to  restore  the  equilibrium. 

Q.  Is  there  an  UPPER  as  well  as  a  LOWER 
CURRENT  in  the  atmosphere  ? 

A.  Yes ;  the  upper  current  of  rare- 
fied air  is  from  tfie  equator  to  the  poles  ; 
where  it  is  condensed — and  then  returns 
again  to  the  equator,  forming  the  lower 
current. 

Q.  These  LOWER  CURRENTS  (from  the  poles  to 
the  equator)  have  an  EASTERLY  tendency.  Explain, 
the  cause  of  this. 

A.  All  the  atmosphere  revolves  with 
the  earth ;  but  when  a  current  of  air  from 
the  poles  flows  towards  the  equatw,  it 
comes  to  a  part  of  the  earth's  surface 
which  is  moving  faster  than  itself;  in 
consequence  of  which  it  is  left  behind, 
and  thus  produces  the  effect  of  a  current 
moving  in  the  opposite  direction. 

Thus,  to  a  person  in  a  carriage,  the  hedges  and  trees 
seem  to  be  running  in  an  opposite  direction. 
As  the  circumference  of  the  earth  at  the  equator  is 


POLAR   CURRENTS.  279 

much,  larger  than  the  circumference  of  the  earth  at  the 
poles,  therefore  every  spot  of  the  earth's  equatorial  surface 
must  move  much,  faster  than  the  corresponding  one  at  the 
poles. 

N.  B.  As  the  earth  revolves  on  its  axis  from  west  to 
east,  therefore  the  air  which  is  carried  with  it  will  seem 
to  blow  from  the  west:  As,  however,  the  current  of  air  from 
the  poles  seems  to  blow  in  the  opposite  direction,  it  will 
seem  to  blow  from  the  east  (or  to  be  an  easterly  wind). 

Q.  By  what  means  are  the  north-east  and 
south-east  TRADE  WINDS  produced  ? 

A.  By  a  combination  of  the  two  mo- 
tions of  the  polar  currents :  which  pro- 
duces the  intermediate  directions  of  the 
north-east  and  south-east. 

Q.  Are  BOTH  these  motions  of  the  polar  currents 
REAL? 

A.  No.  The  motion  from  the  east 
to  west  is  only  apparent.  As  the  earth 
revolves  from  west  to  east,  the  air  carried 
with  it  will  be  a  west  wind  ;  but  the  polar 
currents  seem  to  blow  in  the  opposite 
direction,  merely  because  they  have  not 
acquired  the  same  velocity. 

Q.  Do  trade  winds  blow  from  the  north-east 
and  south-east  ALL  the  YEAR  ROUND  ? 

A.  Yes,  in  the  open  sea;  that  is,  in 
the  Atlantic  and  Pacific  Oceans,  for  about 
30°  each  side  of  the  equator. 

Q.  What  do  the  north-easterly  and  south-east- 
erly  trade  winds  produce  when  they  meet  near  the 
equator  ? 

A.     A  region  of  calms,  in  which  thick 


WIND. 

foggy  a^r  prevails,  with  sudden  showers 
and  thunder-storms. 

Q.      Is  this  region  of  calms  FIXED  in  its  position  ? 

A.  No;  it  shifts  its  place  according 
to  the  sun's  distance,  and  position  in 
regard  to  the  equator :  being  sometimes 
entirely  to  the  north  of  the  equator,  and 
occasionally  reaching  as  far  as  2°  south 
of  it. 

Q.  Do  the  TRADE  WINDS  blow  uniformly  from 
north-east  and  south-east  in  the  INDIAN  OCEAN  ? 

A.  No ;  nor  yet  in  those  parts  of  the 
Atlantic  and  Pacific  which  verge  on  the 
continents. 

Q.  How  do  the  TRADE  WINDS  in  the  INDIAN 
OCEAN  blow  ? 

A.  From  April  to  October  a  south- 
west wind  prevails ;  but  from  October  to 
April,  a  north-east. 

Q.  What  are  these  periodical  currents  of  air 
(which  affect  the  neighborhood  of  the  Arabian,  In- 
dian, and  Chinese  Seas)  called  ? 

A.     They  are  called  MONSOONS. 

Q.  How  far  do  the  limits  of  the  MONSOONS  ex- 
tend? 

A.  They  extend  from  the  African 
shore  to  the  longitude  of  New  Guinea ; 
and  are  felt  northward  as  far  as  the 
parallel  of  latitude,  which  crosses  the 
Loochoo  Isles. 


MONSOONS.  281 

The  Loochoo  Isles  are  about  24°  north  latitude,  and 
130°  east  longitude. 

Q.  Why  do  not  the  trade  winds  in  the  INDIAN 
OCEAN  blow  south-west  from  April  to  October? 

A.  Because  the  air  of  Arabia,  Persia, 
India,  and  China,  is  so  rarefied  by  the 
enormous  heat  of  their  summer  sun, 
that  the  cold  air  from  the  south  rushes 
towards  these  nations,  across  the  equator, 
(during  these  six  months,)  and  produces 
a  SOUTH-WEST  wind. 

Q.  To  what  distance  does  this  SOUTH-WEST 
wind  prevail  ? 

A.  From  3°  south  of  the  equator,  to 
the  shores  of  the  Arabian,  Indian,  and 
Chinese  Seas. 

Q.  Why  do  the  trade  winds  (in  the  INDIAN 
OCEAN)  blow  north-east  from  October  to  April? 

A.  Because  the  southern  part  of  the 
torrid  zone  is  most  heated,  when  the  sun 
has  left  the  northern  side  of  the  equator 
for  the  southern :  and  the  cold  air  from 
the  north  (rushing-  towards  the  southern 
tropic)  is  diverted  into  the  direction  of 
NORTH-EAST,  where  it  continues  for  the 
other  six  months  of  the  year. 

Q.  Are  the  monsoons  as  POWERFUL  as  the 
trade  winds  ? 

A.  They  are  far  more  so,  and  very 
often  amount  to  violent  gales. 


282  WIND. 

Q.  Why  are  the  MONSOONS  more  USEFUL  to  the 
mariner  than  the  fixed  TRADE  WINDS  ? 

A.  Because  the  mariner  is  able  to 
avail  himself  of  these  periodic  changes, 
to  go  in  one  direction  during  one  half  of 
the  year,  and  to  return  in  the  opposite  di- 
rection during  the  other  half. 

Q.       How  is  the  change  of  the  monsoons  marked  ? 

A.  By  an  interval  of  alternating  calms 
and  storms.  ^ 

Q.  When  are  the  WINDS  at  the  NORTH  general- 
ly the  HIGHEST  ? 

A.  The  winds  in  December  and  Jan- 
uary are  generally  the  highest. ;  Those 
in  February  and  November  the  next ; 
and  those  in  August  and  September  are 
the  least  boisterous. 

Q.  Why  are  the  winds  at  the  North  generally 
HIGHEST  in  DECEMBER  and  JANUARY  ? 

A.  Because  the  sun  is  farthest  south 
in  those  months;  and  (as  the  heat  in 
these  northern  regions  rapidly  decreases) 
the  contrast  between  our  temperature 
and  that  of  the  torrid  zone  is  greater  in 
December  and  January,  than  in  any 
other  two  months  throughout  the  year. 

Q.  Why  does  this  CONTRAST  of  heat  increase 
the  VIOLENCE  of  the  WIND  ? 

A.  Because  the  air  always  seeks  to 
preserve  an  equilibrium;  therefore  the 


THE    GOODNESS    OP    GOD.  283 

greater  the  contrast,  the  more  violent 
will  be  the  rush  of  air  to  equalize  the 
two  volumes. 

Q.  Why  are  the  winds  at  the  North  generally 
most  PLACID  during  the  months  of  SEPTEMBER  and 
AUGUST  1 

A.  Because  August  and  September 
are  the  warmest  months,  when  we  ap- 
proach nearest  to  the  heat  of  the  torrid 
zone ;  therefore  the  air  (to  and  from  the 
equator)  moves  with  less  velocity  in  our 
northern  hemisphere  in  those  two  months 
than  in  any  other. 

Q.  Show  the  GOODNESS  and  WISDOM  of  GOD  in 
this  constant  tendency  of  air  to  equilibrium. 

A.  If  the  torrid  zone  were  not  tem- 
pered by  cold  air  from  the  polar  regions, 
it  would  become  so  hot,  that  no  human 
being  could  endure  it.  If  (on  the  other 
hand)  the  polar  regions  were  never 
warmed  by  hot  air  from  the  torrid  zone, 
they  would  soon  become  insufferably 
cold. 

Q.  In  what  OTHER  way  does  the  mingling  of 
the  polar  and  equatorial  atmosphere  act  BENEFICIAL- 
LY? 

A.  In  the  equatorial  regions,  the 
great  abundance  of  vegetable  life  is  pro- 
ductive of  a  very  large  amount  of  oxy- 
gen: In  the  colder  regions,  artificial  Jires 


284  WIND. 

and  dense  masses  of  animal  life,  produce 
large  quantities  of  carbonic  acid:  The 
mingling  of  the  polar  and  equatorial 
atmosphere  assists  in  supplying  each  of 
these  regions  with  the  very  gas  in  which 
it  would  be  otherwise  defective. 

Q.  How  does  the  mingling  of  the  POLAR  and 
EQUATORIAL  atmosphere  serve  to  supply  each  region 
with  the  GAS  it  most  requires  ? 

A.  The  plants  of  the  EQUATORIAL  re- 
gions require  carbonic  acid; — The  ani- 
mals of  the  COLDER  regions  require 
oxygen  : — The  currents  of  air  from  the 
Poles  carry  carbonic  acid  to  the  equato- 
rial plants ;  and  the  currents  of  air  from 
the  JEquator  carry  oxygen  to  the  animals 
which  abound  nearer  the  poles. 

Q.  Why  are  EAST  WINDS  in  Europe,  and 
WEST  WINDS  in  the  United  States,  generally  DRY  1 

A.  Because  they  come  over  vast  con- 
tinents, and  therefore  absorb  very  little, 
water;  and  being  thirsty,  they  readily 
imbibe  moisture  from  the  air  and  clouds, 
and  therefore  bring  dry  weather. 

Q.       Why  is  the  NORTH  WIND  generally  COLD  ? 

A.  Because  it  comes  from  the  polar 
regions,  over  mountains  of  snow  and 
seas  of  ice. 

Q.  Why  are  NORTH  WINDS  generally  DRY  and 
btiing  ? 


NORTH    AND    SOUTH    WINDS.  285 

A.  Because  they  come  from  colder 
regions,  and  being1  warmed  by  the  heat 
of  our  climate,  absorb  moisture  from 
every  thing*  they  touch ;  in  consequence 
of  which,  they  are  both  dry  and  parch- 
ing. 

Q.       Why  are  SOUTH  WINDS  generally  WARM  ? 

A.  Because  they  come  from  the  tor- 
rid zone,  where  they  are  much  heated. 

Q.       Why  do  SOUTH  WINDS  often  bring  RAIN  ? 

A.  Because,  coming-  from  the  torrid 
zone,  they  are  much  heated,  and  imbibe 
water  very  plentifully,  as  they  pass  over 
the  Ocean. 

Q.  How  docs  this  account  for  the  RAINY  cha- 
racter of  SOUTH  winds  ? 

A.  As  soon  as  they  reach  a  cold  cli- 
mate they  are  condensed,  and  can  no 
longer  hold  all '  their  vapor  in  suspen- 
sion ;  in  consequence  of  which,  some  of 
it  is  deposited  as  rain. 

Q.  Why  are  WEST  WINDS  in  Europe,  and 
EAST  WINDS  in  the  United  States,  generally  RAINY  ? 

A.  Because  they  come  over  the 
Atlantic  Ocean,  and  are  laden  with 
vapor ;  if,  therefore,  they  meet  with  the 
least  chill,  some  of  the  vapor  is  deposited 
as  rain. 

Q.       Why  is  a  fine,  CLEAR  DAY  sometimes 
CAST  in  a  few  minutes  1 


286  WIND. 

A.  Because  some  sudden  change  of 
temperature  has  condensed  the  vapor  of 
the  air  into  clouds. 

Q.  Why  are  CLOUDS  sometimes  DISSIPATED  very 
suddenly  ? 

A.  Because  some  dry  wind  (blowing 
over  the  clouds)  imbibes  their  moisture, 
and  carries  it  off  in  invisible  vapor. 

Q.       Why  do  SOUTH-EAST  winds  bring  us  RAIN  ? 

A.  Because  they  come  from  the  tor- 
rid zone,  and  get  laden  with  vapor  in 
their  transit  across  the  ocean.  But  when 
they  reach  our  colder  climate,  (being 
condensed  by  the  chill)  some  of  the  va- 
por is  precipitated  in  rain. 

Q.       Why  do  NORTH-WEST  winds  RARELY  bring 

RAIN? 

A.  Because  they  come  from  a  climate 
colder  than  our  own,  and  their  capacity 
for  imbibing  vapor  is  increased,  when 
they  reach  a  warmer  climate  ;  in  conse- 
quence of  which,  north-west  winds  dry 
the  air,  dispel  the  clouds,  and  promote 
evaporation. 

Q.  Why  does  WIND  sometimes  bring  RAIN  and 
sometimes  FINE  weather  ? 

A.  If  the  wind  be  colder  than  the 
clouds,  it  will  condense  their  vapor  into 
rain:  But  if  the  wind  is  ivarmer  than 


MARCH    WINDS.  287 

the  clouds,  it  will  dissolve  them,  and  cause 
them  to  disappear. 

Q.       What  is  the  USE  of  dry  MARCH  winds  ? 

A.  They  dry  the  soil,  which  is  satu- 
rated with  the  floods  of  February,  break 
up  the  heavy  clods,  and  fit  the  land  for 
the  seed  committed  to  it. 

Q.  Why  is  it  said,  that  "  MARCH  COMES  IN 
like  a  LION  ?" 

A.  Because  it  comes  in  with  bluster- 
ing winds,  so  essential  to  dry  the  soil, 
lest  it  rot  the  seeds  committed  to  it. 

Q.       Why  does  "  MARCH  GO  OUT  like  a  LAMB  ?" 

A.  Because  the  water  (evaporated 
by  the  high  winds)  falls  again  in  showers, 
to  fertilize  the  earth  ;  and  these  constant 
showers  break  the  violence  of  the  winds. 

Q.  Why  is  it  said,  that  "  A  bushel  of  MARCH 
DUST  is  worth  a  king's  ransom .?" 

A.  Because  it  indicates  that  there 
has  been  a  continuance  of  dry  weather  ; 
and  unless  March  be  dry,  the  seed  will 
rot  in  the  wet  soil. 

Q.  Why  is  it  said,  "A  DRY,  cold  MARCH 
never  BEGS  BREAD?" 

A.  Because  the  dry,  cold  winds  of 
March  prepare  the  soil  for  seeds  ;  which 
germinate  and  produce  fruit  in  the 
autumn. 


288  WIND. 

Q.  It  is  said,  that  "A  WET  MARCH  makes  a 
SAD  autumn."  Explain  the  reason  of  this. 

A.  If  March  is  wet,  so  much  seed 
rots  in  the  ground,  that  the  autumn  crops 
are  spoiled. 

Q.  It  is  said,  that  "  MARCH  FLOWERS  make 
NO  summer  BOWERS."  Explain  the  reason  of  this. 

A.  If  the  spring  be  very  mild,  vege- 
tation gets  too  forward,  and  is  pinctied 
by  the  nightly  frosts,  so  as  to  produce 
neither  fruits  nor  flowers. 

Q.  It  is  said,  "  A  LATE  SPRING  makes  a  FRUIT- 
FUL YEAR."  Explain  the  reason  of  this. 

A.  If  the  vegetation  of  spring  be 
backward,  the  frosty  nights  will  do  no 
harm;  for,  the  fruits  and  flowers  will 
not  put  forth  their  tender  shoots,  till  the 
nights  become  too  warm  to  injure  them. 

Q.  Why  is  it  said,  that  "  APRIL  SHOWERS 
bring  MAY  FLOWERS  ?" 

A.  Because  April  showers  supply 
the  principal  nourishment,  on  which 
seeds  depend  for  their  development. 

Before  seeds  can  germinate,  three  things  are  essential : — 
Darkness,  Heat,  and  Moisture. 

Q.  Does  RAIN-WATER  possess  any  fertilizing 
properties,  BESIDES  that  of  mere  MOISTURE  ? 

A.  Yes  ;  rain-water  contains  an 
abundance  of  carbonic  acid,  and  a  small 
quantity  of  ammonia;  to  which  much 
of  its  fertilizing  power  may  be  attributed. 


RAIN.  289 

Ammonia  is  a  compound  of  nitrogen  and  hydrogen. 
Common  hartshorn  is  only  ammonia  and  water. 

Q.  Why  is  there  MORE  rain  FROM.  SEPTEMBER 
to  MARCH,  than  from  March  to  September? 

A.  Because  the  temperature  of  the 
air  is  constantly  decreasing;  on  which 
account,  its  capacity  for  holding  vapor  is 
on  the  decrease,  and  the  vapor  is  precip- 
itated as  rain. 

Q.  What  good  purpose  is  effected  under  PROVI- 
DENCE by  this  increase  of  rain  in  AUTUMN  and  WIN- 
TER ? 

A.  Because  rain  hastens  the  putre- 
faction of  the  fallen  leaves;  and  this 
makes  the  earth  fertile. 

Q.  Why  is  there  LESS  rain  FROM  MARCH  to 
SEPTEMBER,  than  from  September  to  March  ? 

A.  Because  the  temperature  of  the 
air  is  constantly  increasing ;  on  which 
account  its  capacity  for  holding  vapor  is 
on  the  increase,  and  very  little  is  precipi- 
tated as  rain. 

Q.  Why  is  the  RISING  SUN  in  summer  accom- 
panied with  a  BREEZE  ? 

A.  Because  the  heat  of  the  rising* 
sun  stops  the  radiation  of  heat  from  the 
earth,  and  warms  its  surface. 

Q.      How  does  this  WARMTH  produce  a  BREEZE  ? 

A.  The  air  (resting  on  the  earth's 
surface)  being  warmed  by  contact  ascends, 
13 


290  WIND. 

<  '.       •--.,', 

and  colder  air  rushing  in  to  fill  up  the 
void,  produces  the  morning  breeze. 

Q.  Why  is  there  often  an  EVENING  BREEZE 
during  the  summer  months  ? 

A.  Because  the  earth  radiates  heat 
at  sun-set  and  the  air  is  rapidly  cooled 
down  by  contact  :  this  condensation 
causes  a  motion  in  the  air,  called  the 
evening*  breeze. 

Q.  Why  are  TROPICAL  ISLANDS  subject  to  a 
SEA  BREEZE  every  MORNING  :  (i.  e.,  a  breeze  blowing 
from  the  sea  to  the  land)  ? 

A.  Because  solar  rays  are  unable  to 
heat  the  surface  of  the  sea,  as  they  do 
the  earth ;  therefore,  the  air  resting  on  the 
sea  is  less  heated  than  the  air  resting  on 
the  earth  ;  and  the  colder  sea  air  blows 
inland  to  restore  the  equilibrium. 

Q.   Why  is  a  LAND  BREEZE  UNHEALTHY  ? 

A.  Because  it  is  frequently  laden 
with  exhalations  from  putrefying  ani- 
mal and  vegetable  substances. 

Q.       Why  is  a  SEA  BREEZE  fresh  and  HEALTHY  ? 

A.  Because  it  passes  over  the  fresh 
sea,  and  is  not  laden  with  noxious  ex- 
halations. 

It  is  particularly  healthy,  therefore,  to  walk  on  the  sea- 
beach  before  ten* o'clock  in  the  morning;  but  unhealthy 
after  sun-set. 

Q.  Why  is  there  generally  a  fresh  breeze  from 
the  SEA  during  the  summer  and  autumn  MORNINGS  ? 


SEA    AND    LAND    BREEZES.  291 

A.  Because  land  is  more  heated  by 
the  sun  than  the  sea  is;  and  the  land  air 
becomes  hotter  than  that  over  the  sea  ; 
in  consequence  of  which,  the  cooler  sea 
air  glides  inland  to  restore  the  equili- 
brium. 

Q.       Why  does  a  SEA  BREEZE  feel  COOL  ? 

A.  Because  the  sun  cannot  make  the 
surface  of  the  sea  so  hot  as  the  land; 
therefore,  the  air  which  blows  from  the 
sea  is  cooler  than  t/ie  air  of  the  land. 

Q.  Why  are  TROPICAL  ISLANDS  subject  to  a 
LAND  BREEZE  every  EVENING  (i.  e.,  a  breeze  blowing 
from  the  land  towards  the  sea)  ? 

A.  Because  the  surface  of  the  land 
cools  down  faster  (after  sun-set)  than 
the  surface  of  the  sea :  in  consequence 
of  which,  the  air  of  the  cold  land  is  con- 
densed — sinks  down — and  spreads  itself 
into  the  warmer  sea  air — causing  the 

LAND  BREEZE. 

Q.       Why  is  the  LAND  BREEZE  COOL  ? 

A.  Because  the  surface  of  'the  land 
is  cooled  at  sun-set  quicker  than  the  sur- 
face of  the  sea ;  therefore,  seamen  feel 
the  air  from  the  land  to  be  chill. 

Q.  Why  is  Ike  TEMPERATURE  of  ISLANDS  mor6 
EQUABLE  than  that  of  CONTINENTS  ? 

A.  Because  the  water  around  the  isl- 
and absorbs  the  extreme  heat  of  sum- 


292  WIND. 

mer;  and  gives  out  heat  to  mitigate  the 
extreme  cold  of  winter. 

Q.  ISLANDS  are  WARMER  in  winter  than  conti- 
nents. Explain  the  reason  of  this. 

A.  Unless  the  sea  be  frozen  (which 
is  rarely  the  case)  it  is  warmer  than  the 
frozen  land :  and  the  warmth  of  the  sea 
air  helps  to  mitigate  the  intense  cold  of 
the  land  air. 

Q.      Explain  the  cause  of  sea  WAVES  ? 

A.  The  wind  (acting  on  the  surface 
of  the  sea)  piles  up  ridges  of  water, 
leaving  behind  an  indentation :  as  the 
water  on  all  sides  rushes  to  Jill  up  this 
indentation,  the  disturbance  spreads  on 
all  sides,  and  billow  rolls  after  billow. 

Q.       Why  does  WIND  generally  feel  COLD  ? 

A.  Because  a  constantly  changing 
surface  comes  in  contact  with  our  body, 
to  draw  off  its  heat. 

Q.  Why  is  a  ROOM  (even  without  a  fire)  ge- 
nerally WARMER  than  the  OPEN  AIR  ? 

A.  Because  the  air  in  a  room  is  not 
subject  to  much  change,  and  soon  becomes 
of  the  same  temperature  as  our  skin, 
when  it  no  longer  feels  cold. 

Q.  Why  do  we  generally  feel  COLDER  out-of- 
doors  than  in-doors  ? 

A.  Because  the  air  (which  surrounds 
us)  is  always  changing ;  and  as  fast  as 


COOLING.  293 

one  portion  of  air  has  become  warmer 
by  contact  \vith  our  body,  another  colder 
portion  surrounds  us,  to  absorb  more 
heat. 

Q.  How  does  BLOWING  HOT  FOOD  make  it 
COOL? 

A.  It  causes  the  air  (which  has 
been  heated  by  the  food)  to  change  more, 
rapidly,  and  give  place  to  fresh  cold  air. 

Q.  Why  do  ladies  FAN  THEMSELVES  in  hot 
weather  ? 

A.  That  fresh  particles  of  air  may  be 
brought  in  contact  with  their  faces  by 
the  action  of  the  fan ;  and  as  every 
fresh  particle  of  air  absorbs  some  heat 
from  the  skin,  this  constant  change 
makes  them  cool. 

Q.       Does  a  fan  COOL  the  AIR  ? 

A.  No ;  it  makes  the  air  hotter  by 
imparting  to  it  the  heat  out  of  our  face  ; 
but  it  cools  our  face  by  transferring  its 
heat  to  the  air. 

Q.      How  fast  does  wind  travel  ? 

A.  A  gentle  breeze  goes  at  about 
the  rate  of  5  miles  an  hour.  A  high 
wind  from  20  to  60.  A  hurricane  from 
80  to  100  miles  an  hour. 

Q.      How  is  the  VELOCITY  of  WINDS  ascertained? 

A.     By  observing  the  velocity  of  the 


294  WIND. 

clouds;  and  by  an  instrument  for  the 
purpose,  called  an  Anemometer. 

•  Pronounce  An-e-mom'-e-ter.  From  two  Greek  words 
avefiog  (wind)  and  /aer^oi/  (a  measure).  This  term  is  applied 
more  frequently  to  an  instrument  which  measures  the  farce 
of  wind. 

Q.  How  is  the  VELOCITY  of  the  CLOUDS  ascer- 
tained ? 

A.  By  observing-  the  speed  of  their 
shadow  along-  the  ground;  which  is 
found  (in  a  high  wind)  to  vary  from  20 
to  60  miles  an  hour. 

Q.  Why  is  there  a  strong  DRAUGHT  through 
the  KEVHOLE  of  a  door  ? 

A.  Because  the  air  in  the  room  we 
occupy  is  warmer  than  the  air  in  the 
hall ;  therefore,  the  air  from  the  hall 
rushes  through  tlie  keyhole  in  the  room, 
and  causes  a  draught. 

Q.  Why  is  there  a  strong  DRAUGHT  UNDER  the 
DOOR,  and  through  the  crevice  on  each  side  ? 

A.  Because  cold  air  rushes  from  the 
hall,  to  supply  the  void  in  the  room, 
caused  by  the  escape  of  warm  air  up 
the  chimney,  &c. 

Q.  Why  is  there  always  a  DRAUGHT  through 
the  WINDOW  crevices  ? 

A.  Because  the  external  air  (being 
colder  than  the  air  of  the  room  we  occu- 
py) rushes  through  the  window  crev- 
ices to  supply  the  deficiency,  caused  by 


DRAUGHT — VENTILATION.  295 

the  escape  of  warm  air  up  the  chimney, 
&c. 

Q.  If  you  open  the  LOWER  SASH  of  a  window, 
there  is  more  DRAUGHT  than  if  you  open  the  UPPER 
sash.  Explain  the  reason  of  this. 

A.  If  the  lower  sash  be  open,  cold 
external  air  will  rush  freely  into  the  room 
and  cause  a  great  draught  inwards ; 
But  if  the  upper  sash  be  open,  the  heat- 
ed air  of  the  room  will  rush  out,  and  (of 
course)  there  will  be  less  draught  in- 
wards. 

Q.  By  which  means  is  a  ROOM  better  VENTI- 
LATED— By  opening  the  upper  or  the  lower  sash  ? 

A.  A  room  is  better  ventilated  by 
opening  the  upper  sash ;  because  the  hot 
vitiated  air  (which  always  ascends  to- 
wards the  ceiling)  can  escape  more  easily. 

Q.  By  which  means  is  a  HOT  ROOM  more 
quickly  COOLED — By  opening  the  upper  or  the  lower 
sash  ? 

A.  A  hot  room  is  cooled  more  quickly 
by  opening  the  lower  sash ;  because  the 
cold  air  can  enter  more  freely  at  the 
lower  part  of  the  room,  than  at  the  upper. 

Q.       Why  does  WIND  DRY  damp  LINEN  ? 

A.  Because  dry  wind  (like  a  dry 
sponge)  imbibes  the  particles  of  vapor 
from  the  surface  of  the  linen,  as  fast  as 
they  are  formed. 


296  BAROMETER. 

Q.  Which  is  the  HOTTEST  PLACE  in  a  church, 
chapel,  or  theatre? 

A.     The  gallery. 

Q.  Why  is  the  GALLERY  of  all  public  places 
HOTTER  than  the  LOWER  parts  of  the  building  ? 

A.  Because  the  heated  air  of  the 
building*  ascends;  and  all  the  cold  ait 
(which  can  enter  through  the  doors  and 
windows)  keeps  to  the  floor ',  till  it  has  be- 
come heated. 

Q.  Why  do  PLANTS  often  grow  out  of  WALLS 
and  TOWERS  ? 

A.  Because  the  seed  has  been  blown 
there  with  the  dust,  by  the  wind,  or 
dropped  by  some  bird  flying  over.p 

£5 


BAROMETER 

CHAPTER  XXV. 

Q.       What  is  a  BAROMETER? 

A.  A  weather-glass,  or  instrument  to 
measure  the  variations  in  the  weight  of  the 
air ;  by  means  of  which  variations,  we 
may  judge  what  weather  may  be  ex- 
pected. 

BAROMETER  is  a  compound  of  two  Greek  words, 
(weight)  and  perpov  (a  measure). 

Q.       What  is  a  THERMOMETER? 


BAROMETER.  297 

A.  An  instrument  to  show  how  hot 
or  cold  anything  is. 

THERMOMETER  is  a  compound  of  two  Greek  words  Qep- 
p$  (heat)  and  perpov  (measure). 

Q.  What  is  the  DIFFERENCE  between  a  THER- 
MOMETER and  a  BAROMETER  ? 

A.  In  a  THERMOMETER  the  mercury 
is  sealed  up  from  the  air ;  and  rises  or 
falls,  as  the  varying1  temperature  of  the 
air  expands  or  contracts  it :  but 

In  a  BAROMETER  the  mercury  is  left 
exposed  (or  open)  to  the  air  ;*  and  rises 
or  falls,  as  the  varying*  weight  of  the  air 
presses  upon  the  open  column. 

Q.  If  the  mercury  of  the  thermometer  be  SEALED 
up/r0w  the  air,  how  can  the  air  AFFECT  it? 

A.  The  heat  of  the  air  passes  through 
the  glass  tube  into  the  mercury  which 
causes  the  metal  to  expand  and  rise  in 
the  tube. 

Q.       Why  is  the  TUBE  of  a  barometer  left  OPEN  ? 

A.  That  the  air  may  press  upon  it 
freely ;  and,  as  this  pressure  varies,  the 
mercury  rises  or  falls  in  the  tube. 

The  top  of  the  tube  must  be  a  "vacuum,-"  otherwise 
the  pressure  of  the  external  air  upon  the  lower  part  of  the 
column  cannot  affect  the  mercury. 

Q.  How  can  a  barometer,  which  measures  the 
WEIGHT  of  air,  be  of  service  as  a  WEATHER  glass  ? 

*  At  its  lower  extremity. 


298  BAROMETER. 

A.  When  air  is  moist,  or  filled  with 
vapor,  it  is  lighter  than  usual ;  and  the 
column  of  mercury  stands  low  : 

When  air  is  dry  and  free  from  vapor, 
it  is  heavier  than  usual ;  and  the  mercury 
stands  high :  Thus  the  barometer  (by 
showing*  the  variations  in  the  weight  of 
tlie  air)  indicates  the  changes  of  the 
weather  also. 

Q.  Why  can  you  tell  (by  looking  at  a  BA- 
ROMETER) what  KIND  of  WEATHER  it  will  be  1 

A.     Because  the  mercury  in  the  tube 
rises  and  falls,  as  the  air  becomes  heav- 
ier or  lighter :  and  we  can  generally  tell 
*by  the  weight  of  the  air,  what  kind  of 
^weather  to  expect. 

Q.      Does  the  WEIGHT  of  the  air  VARY  MUCH? 
A.     Yes ;  the   atmosphere  varies   as 
>.much  as  one-tenth  part  more  or  less. 

-Q.       What  USE  is  a  BAROMETER  to  sailors  ? 

A.     It  warns   them  to  regulate  their 
before  squalls  come  on. 

Q.  How  can  a  BAROMETER  warn  SAILORS  to 
regulate  their  SHIPS  ? 

A.  As  it  indicates  when  wind,  rain, 
and  storm  are  at  hand,  the  sailor  can 
make  his  ship  trim  before  they  overtake 
him. 

Q.  Are  there  any  RULES  which  can  be  depended 
on? 


BAROMETER.  299 

A.  Yes ;  there  are  ten  special,  rules 
to  direct  us  how  to  know  the  changes 
of  weather,  by  marking  the  mercury  of 
a  barometer. 

Q.  Mention  the  IST  SPECIAL  RULE  with  regard 
to  the  barometer  ? 

A.  The  barometer  is  highest  of  all 
during  a  long  frost;  and  it  generally 
rises  with  a  north-west  wind. 

Q.  Why  is  the  barometer  HIGHEST  of  all  during 
a  long  FROST  ? 

A.  Because  a  long  frost  condenses  the 
air  very  greatly ;  and  the  move  condensed 
air  is,  the  greater  is  its  pressure  on  the 
mercury  of  a  barometer. 

Q.  Why  does  the  barometer  generally  RISE 
with  NORTH  WEST  winds  ? 

A.  Because  NORTH-WEST  winds  make 
the  air  both  cold  and  dry :  and  being 
both  condensed,  and  without  vapor,  it  is 
much  heavier, 

Q.       Mention  the  2o  SPECIAL  RULE  with  regard 

to  the  barometer  ? 

A.  The  barometer  is  lowest  of  all 
during  a  thaw,  which  follows  a  long  frost : 
and  it  generally  falls  with  SOUTH  or 
EAST  wind. 

Q.       Why  does  the  barometer  fall  LOWEST  of  all 

<Lt  the  BREAKING    UP  of  a  long  FROST  ? 

A.     1st — Because  the  air  (which  had 


300  BAROMETER. 

been  much  dried  by  the  frost)  absorbs 
the  moisture  of  the  fresh  warm  current 
of  wind  from  the  south  or  south-west : 
and 

2dly — The  air  (which  had  been  much 
condensed  by  the  frost)  is  suddenly  ex- 
panded by  the  warm  wind,  which  is 
introduced. 

Q.  Why  does  the  barometer  fall  very  low  with 
SOUTH  and  EAST  winds  ? 

A.  Because  SOUTH  and  EAST  winds 
come  heavily  laden  with  vapor  ;  and  va- 
porized air  is  lighter  than  dry  air. 

Q.       What  effect  has  WIND  on  the  mercury  ? 

A.  The  barometer  is  high,  when  the 
wind  blows  between  the  WEST  and  the 
NORTH;  but  it  is  low,  when  the  wind 
blows  between  the  SOUTH  and  the  EAST. 

Q.  WHY  do  these  winds  affect  the  mercury  of  a 
barometer  ? 

A.  Because  the  pressure  of  the  air  is 
increased  by  cold  winds,  and  diminished 
by  warm  ones. 

Q.  Why  is  the  pressure  of  air  INCREASED  with 
cold  winds  from  the  NORTH  ? 

A.  Because  the  air  contracts,  when 
it  is  cooled  by  winds  from  the  north  and 
east,  and  warmer  air  flows  in  from  all 
sides  to  fill  up  the  vacuum;  in  conse- 


BAROMETER.  301 

quence  of  which,  its  volume  is  increased, 
and  the  barometer  rises. 

Q.  Why  i$  the  PRESSURE  of  air  DIMINISHED 
by  warm  winds  from,  the  SOUTH? 

A.  Because  the  air  ascends  when  it  is 
heated  by  south  winds,  and  flows  away 
in  all  directions ;  in  consequence  of 
which,  its  volume  is  diminished,  and  the 
mercury  falls. 

Q.  What  is  the  3o  SPECIAL  RULE  with  regard 
to  the  barometer  ? 

A.  While  the  barometer  stands  above 
30,  the  air  must  be  very  dry,  or  very 
cold,  or  perhaps  both — and  no  rain  may 
be  expected. 

Q.  Why  will  there  be  NO  RAIN  if  the  Am'be 
very  DRY  ? 

A.  Because  dry  air  will  absorb  mois- 
ture, and  not  part  with  it  in  rain. 

Q.  Why  will  there,  be  NO  RAIN  if  the  AIR  be 
very  COLD  ? 

A.  Because  it  is  so  much  condensed, 
that  it  has  already  parted  with  as  much 
moisture  as  it  can  spare. 

Q.  What  is  the  4xn  SPECIAL  RULE  with  regard 
to  the  barometer? 

A.  When  the  barometer  stands  very 
low  indeed,  there  will  never  be  much 
rain  ;  although  a  fine  day  will  seldom 
occur  at  such  times. 


302  BAROMETER. 

Q.  What  kind  of  WEATHER  is  there  likely  to 
be,  when  the  barometer  is  UNUSUALLY  LOW? 

A.  S'tort  heavy  showers,  with  sudden 
squalls  of  wind  from  the  wM. 

Q.  Why  will  there  be  VERY  LITTLE  RAIN,  if 
the  barometer  is  UNUSUALLY  LOW  1 

A.  Because  the  air  must  be  very 
warm,  or  very  moist,  or  perhaps  both. 

Q.  Why  will  there  be  little  or  no  rain,  if  the 
AIR  be,  very  WARM  ? 

A.  Because  warm  air  has  a  tenden- 
cy to  imbibe  more  moisture  and  not  to 
part  with  what  it  has. 

Q.  Why  will  there  be  little  or  no  rain,  if  the 
air  be  MOIST  and  the  barometer  very  LOW  ? 

A.  Because  rain  will  never  fall  (even 
though  the  air  be  saturated),  till  cold  air 
has  been  introduced  to  condense  the  va- 
por :  And,  as  soon  as  cold  air  has  been 
introduced,  the  barometer  will  rise  in- 
stantly. 

Q  Name  the  5ra  SPECIAL  RULE  with  regard 
to  the  barometer  ? 

A.  In  summer-time  (after  a  long  con- 
tinuance of  fair  weather)  the  barometer 
w\\\fall  gradually  for  2  or  3  days  before 
rain  comes :  But  if  the  fall  of  the  mer- 
cury is  very  sudden,  a  thunder-storm  may 
be  expected. 

Q.  What  is  the  GTH  SPECIAL  RULE  with  regard 
to  the  barometer  ? 


BAROMETER.  303 

A.  When  the  sky  is  cloudless,  and 
seems  to  promise  fair  weather — if  the 
barometer  is  low,  the  face  of  the  sky  will 
soon  be  suddenly  overcast. 

Q.  What  is  the  TTH  SPECIAL  RULE  with  regard 
to  the  barometer  ? 

A.  Dark  dense  clouds  will  pass  over 
without  rain,  when  the  barometer  is 
high;  but  if  the  barometer  be  low,  it 
will  often  rain  without  any  appearance  of 
clouds. 

Q.  What  is  the  STH  SPECIAL  RULE  with  regard 
to  the  barometer  ? 

A.  The  higher  the  barometer,  the 
greater  the  probability  of  fair  weather. 

Q.  Why  is  the  barometer  HIGH  in  FINE  wea- 
ther ? 

A.  Because  the  air  in  fine  weather 
contains  very  little  vapor.  The  drier  the 
air,  the  higher  does  the  mercury  of  the 
barometer  rise. 

Q.  What  is  the  QTH  SPECIAL  RULE  with  regard 
to  the  barometer  ? 

A.  When  the  mercury  is  in  a  rising 
state,  fine  weather  is  at  hand  ;  but,  when 
the  mercury  is  in  a  sinking  state,  foul 
weather  is  near. 

Q.  Why  does  the  mercury  RISE  at  the  approach 
of  FINE  weather  ? 

A.     Because  the  air  is  becoming*  more 


304  BAROMETER. 

dry ;   and,  therefore,  its  pressure  is  in- 
creased. 

Q.  Why  does  the  mercury  SINK  at  the  approach 
of  FOUL  weather  ? 

A.  Because  the  air  is  laden  with  va- 
por or  disturbed  by  ivind. 

Q.  Why  does  VAPOR  in  the  air  make  the  mer- 
cury SINK  ? 

A.  Because  vaporized  air  is  lighter 
than  dry  air ;  and  its  pressure  on  the 
barometer  less. 

Q.  What  is  the  lOxn  SPECIAL  RULE  with  re- 
gard to  the  barometer  ? 

A.  If  (in  frosty  weather)  it  begins  to 
snoiv,  the  barometer  generally  rises  to 
30 ;  where  it  remains,  so  long  as  the 
snow  continues  to  fall :  If,  after  this,  the 
weather  clears  up,  you  may  expect  very 
severe  cold. 

Q.  How  can  you  know  if  the  MERCURY  of  the 
barometer  is  RISING  ? 

A.  When  the  top  of  the  column  is 
convex  (i.  e.,  higher  in  the  middle  than  at 
the  sides),  the  mercury  is  in  a  rising  state. 

Q.  How  can  you  tell  if  the  MERCURY  of  the 
barometer  is  FALLING  ? 

A.  When  the  top  of  the  column  is 
concave  (i.  e.,  hollow  in  the  middle),  the 
mercury  is  in  a  falling  state. 

Q.  Why  is  the  mercury  CONVEX  when  it  is 
RISING  ? 


BAROMETER.  305 

A.  Because  the  parts  of  the  mercury 
in  contact  with  the  tube  are  delayed  by 
the  glass ;  in  consequence  of  which,  the 
middle  part  rises  faster  than  the  sides; 
and  the  surface  is  CONVEX. 

Q.       Why  is  the  mercury  CONCAVE  when  it  is 


FALLING  f 


A.  Because  the  parts  of  the  mercury 
in  contact  with  the  tube  are  delayed  by 
capillary  attraction ;  in  consequence  of 
which,  the  middle  part  sinks  faster  than 
the  sides  :  and  the  surface  is  CONCAVE. 

Q.  What  effect  does  a  THUNDER-STORM  produce 
on  the  weather  ? 

A.  It  is  generally  preceded  by  hot 
weather,  and  followed  by  cold  and  show- 
ery weather. 

Q.  What  effect  does  a  SUDDEN  CHANGE  of  tem- 
perature produce  on  the  weather  ? 

A.  A  great  and  sudden  change  (ei- 
ther from  hot  to  cold,  or  from  cold  to 
hot)  is  generally  followed  by  rain  within 
24  hours. 

Q.  Why  is  a  sudden  CHANGE  from  HOT  to 
COLD  followed  by  RAIN? 

A.  Because  cold  condenses  the  air ; 
and  some  of  its  vapor  is  given  off  in 
rain. 

Q.  Why  is  a  sudden  CHANGE  from  COLD  to 
HOT  followed  by  RAIN? 


306  BAROMETER. 

A.  Because  the  air  is  quickly  satu- 
rated with  moisture :  but  when  night 
comes  on,  and  chills  the  temperature, 
some  of  the  abundant  moisture  is  given 
off  in  rain. 

Q.  Why  is  the  air  quickly  SATURATED  with 
MOISTURE,  when  HEAT  rapidly  succeeds  to  COLD  ? 

A.  Because  the  evaporation  (which 
was  checked  by  the  cold)  is  carried  on 
very  rapidly,  in  consequence  of  the  di- 
minished pressure  of  the  air. 

N.  B.  The  Uss  tke  pressure  of  the  air,  the  more  rapid  tte 
evaporation  of  moisture  will  be. 

Q.       When  does  the  barometer  VARY  MOST  ? 

A.     In  winter-time. 

Q.  Why  does  the  barometer  vary  MORE  in 
WINTER,  than  in  suMMER-fme  ? 

A.  Because  the  difference  of  temper- 
ature between  the  torrid  and  temperate 
zones  is  much  greater  in  winter  than  in 
summer:  and  produces  a  greater  dis- 
turbance in  the  state  of  the  air. 

Q.       When  does  the  barometer  VARY  LEAST  ? 

A.     In  summer-time. 

Q.  Why  does  the  barometer  vary  LESS  in  SUM- 
MER than  in  wutTER-time  ? 

A.  Because  the  temperature  of  the 
torrid  and  temperate  zones  in  summer 
is  so  nearly  equal,  that  its  state  is  not 
mucli  disturbed  by  interchange  of  cur- 
rents. 


BAROMETER.  307 

Q,  ~Have  HEAT  and  COLD  any  effect  on  the  ba- 
rometer ? 

A.  No,  not  of  themselves;  but  be- 
cause cold  weather  is  generally  either 
dry,  or  rough  with  north-west  winds, 
therefore  the  mercury  rises  in  cold  wea- 
ther :  And  because  warm  weather  is 
often  moist,  or  fanned  by  south-east 
winds,  therefore  the  mercury  sinks  in 
warm  weather. 

Q.  Why  is  the  mercury  of  a  barometer  LOWER 
in  the  TORRID  than  in  the  FRIGTD  zone  ? 

A.  Because  the  warm  air  of  the  tor- 
rid zone  contains  much  more  vapor  than 
the  condensed  air  of  the  frigid  zone ; 
and  the  moister  the  air,  the  less  is  its 
pressure. 

Q.      In  what  MONTHS  is  the  barometer  HIGHEST  ? 

A.  In  May  and  August ;  then  in 
June,  March,  September,  and  April. 

Q.      In  what  MONTHS  is  the  barometer  LOWEST  ? 

A.  In  November  and  February ;  then 
in  October,  July,  December,  and  Jan- 
uary. 

Q.  Why  is  there  LESS  wet  from  MARCH  to 
AUGUST  than  there  is  from  August  to  March  ? 

A.  Because  the  heat  is  constantly  in- 
creasing ;  arid  the  capacity  of  air  to  ab- 
sorb and  retain  moisture  increases  like- 
wise. 


308  BAROMETER. 

Q.  Why  is  there  MORE  wet  from  AUGUST  to 
MARCH  than  from  March  to  August  ? 

A.  Because  the  heat  is  constantly 
decreasing;  and  the  capacity  of  air  to 
retain  moisture  decreases  also ;  so  that 
although  it  often  rains,  yet  the  air  is 
always  on  the  point  of  saturation. 

Q.  Why  does  the  mercury  of  a  barometer  RISE 
in  a  FROST  ? 

A.  Because  frost  condenses  the  air ; 
and  condensed  air  is  heavier  than  rare- 
fied air. 

Q.  Why  does  the  mercury  of  a  barometer  FALL 
in  a  THAW  ? 

A.  Because  the  air  is  filled  with 
vapor. 

Q.  What  does  a  SUDDEN  rise  or  fall  of  the  ba- 
rometer indicate  ? 

A.  If  the  rise  be  sudden,  fine  wea- 
ther will  not  continue  long* : 

If  the  fall  be  sudden,  foul  weather 
will  riot  continue  long". 

Q.  What  sort  of  weather  may  we  expect,  if  the 
barometer  is  very  FLUCTUATING  ? 

A.  If  the  mercury  fluctuates  much, 
the  weather  will  J3e  very  Changeable  and 
unsettled. 

THE  FALL  OF  THE  BAROMETER. 

In  very  hot  weather,  the  fall  of  the  mercury  denotes 
thunder.  Otherwise,  the  sudden  falling  of  the  barometer 
denotes  high  wind. 


BAROMETER — SNOW.  309 

In.  frosty  weather,  the  fall  of  the  barometer  denotes  thaw. 

If  wet  weather  happens  soon  after  the  fall  of  the  ba- 
rometer, expect  but  little  of  it. 

In  wet  weather,  if  the  barometer  falls,  expect  much  wet. 

In  fair  weather,  if  the  barometer  falls  and  remains  low, 
expect  much  wet  in  a  few  days,  and  probably  wind. 

N.  B.  The  barometer  sinks  lowest  of  all  for  wind  and 
rain  together ;  next  to  that  for  wind,  (except  it  be  an  east 
or  north-east  wind.) 

THE  RISE  OF  THE  BAROMETER. 

In  winter,  the  rise  of  the  barometer  presages  frost.  ' 

Infiosty  weather,  the  rise  of  the  barometer  presages 
snow. 

If  fair  weather  happens  soon  after  the  rise  of  the  ba- 
rometer, expect  but  little  of  it. 

In  wet  weather,  if  the  mercury  rises  high  and  remains 
so,  expect  continued  fine  weather  in  a  day  or  two. 

In  wet  weather,  if  the  mercury  rises  suddenly  very  high, 
fine  weather  will  not  last  long. 

N.  B.  The  barometer  rises  highest  of  all  for  north  and 
west  winds ;  for  all  other  winds  it  sinks. 

THE  BAROMETER  UNSETTLED. 

If  the  motion  of  the  mercury  be  unsettled,  expect  unset- 
tled weather. 

If  it  stand  at  "  MUCH  RAIN  "  and  rise  to  "  CHANGEABLE," 
expect  fair  weather  of  short  continuance. 

If  it  stand  at  "  FAIR  "  and  fall  to  "  CHANGEABLE,"  expect 
foul  weather. 

N.  B.  Its  motion  upwards  indicates  the  approach  of 
fine  weather ;  its  motion  downwards  indicates  the  approach 
of  foul  weather. 


SNOW.    HAIL.    RAIN. 

CHAPTER   XXYI. 

Q.       What  is  SNOW  ? 

A.     The  condensed  vapor  of  the  air 
frozen,  and  precipitated  to  the  earth. 


310 

Q.       What  is  the  CAUSE  of  SNOW  ? 

A.  When  the  air  is  nearly  saturated 
with  vapor,  and  condensed  by  a  current 
of  air  below  freezing  point,  some  of  the 
vapor  is  condensed,  and  frozen  into 
snow. 

A  few  years  ago,  some  fishermen  (who  wintered  at 
Nova  Zembla),  after  they  had  been  shut  up  in  a  hut  for 
several  days,  opemd  the  window,  and  the  cold  external  air 
rushing  in,  instantly  condensed  the  air  of  the  hut,  and  its 
vapor  fell  on  the  floor  in  a  shower  of  snow. 

Q.       Why  does  snowfall  in  WINTER  time  ? 

A.  Because  the  sun's  rays  are  too 
oblique  to  heat  the  surface  of  the  earth ; 
and  (as  the  earth  has  no  heat  to  radiate 
into  the  air)  the  air  is  very  cold. 

Q.       What  is  ike  cause  of  SLEET  ? 

A.  When  flakes  of  snow  (in  their 
descent)  pass  through  a  bed  of  air  above 
freezing  point,  they  partially  melt ;  and 
fall  to  the  earth  as  half-melted  snow,  or 
sleet. 

Q.       What  is  the  USE  of  SNOW  ? 

A.  To  keep  the  earth  warm,  and  to 
nourish  it. 

Q.      Does  snow  keep  the  EARTH  WARM  ? 

A.  Yes,  because  it  is  a  very  bad  con- 
ductor;  in  consequence  of  which,  when 
the  earth  is  covered  with  snow,  its  tem- 
perature very  rarely  descends  bebw 


USE    OF    SNOW.  311 

freezing  point,  even  when  the  air  is  15 
or  20  degrees  colder. 

Q.  WHY  is  SNOW  a  BAD  CONDUCTOR  of  heat 
and  cold  ? 

A.  Because  air  is  confined  and  en- 
tangled among*  the  crystals ;  .and  air  is 
a  very  bad  conductor:  When,  therefore, 
the  earth  is  covered  with  snow,  it  cannot 
throw  off  its  heat  by  radiation. 

Q.  Tell  me  the  words  of  the  PSALMIST  (cxlvii. 
1 6)  respecting  snow  ;  and  explain  what  he  means  ? 

A.  The  Psalmist  says — "The  Lord 
giveth  snow  like  wool ;"  and  he  means, 
not  only  that  snow  is  as  white  as  icool, 
but  that  it  is  also  as  warm  as  wool. 

Q.       Why  is  WOOL  WARM  ? 

A.  Because  air  is  entangled  among* 
the  fibres  of  the  wool ;  and  air  is  a  very 
bad  conductor. 

Q.       Why  is  SNOW  WARM  ? 

A.  Because  air  is  entangled  among 
the  crystals  of  the  snow ;  and  air  is  a 
very  bad  conduct07\ 

Q.       Why  does  SNOW  NOURISH  the  earth  ? 

A.  Because  it  supplies  moisture  con- 
taining* carbonic  acid ;  which  penetrates 
slowly  into  the  soil,  and  insinuates  itself 
through  every  clod,  ridge,  and  furrow. 

Q.      Why  is  there  NO  SNOW  in  SUMMER  time  ? 


312  SNOW — HAIL. 

A.  Because  the  heat  of  the  earth  melts 
it  in  its  descent,  and  prevents  it  from 
reaching-  the  surface  of  the  earth. 

Q.  Why  are  some  MOUNTAINS  ALWAYS  COVER- 
ED with  SNOW  ? 

A.  1st — Because  the  air  on  a  high 
mountain  is  more  rarefied;  and  rarefied 
air  retains  much  heat  in  a  latent  state  : 
and 

2dly — Mountain-tops  are  not  surround- 
ed by  earth,  to  radiate  heat  into  the  air ; 
and,  therefore,  the  snow  is  not  melted 
in  its  descent,  but  falls  on  the  mountain, 
and  lies  there. 

Q.       Why  is  SNOW  WHITE  ? 

A.  Because  it  is  formed  of  an  infinite 
number  of  very  minute  crystals  and 
prisms,  which  reflect  all  the  colors  of  the 
rays  of  light  from  different  points ;  and 
these  colors,  uniting  before  they  meet 
the  eye,  cause  snow  to  appear  white. 

The  same  answer  applies  to  salt,  loaf-sugar,  &c.    (Set 
p.  372.) 

Q.       What  is  HAIL  ? 

A.  Rain,  which  has  passed  in  its 
descent  through  some  cold  bed  of  air,  and 
has  been  frozen  into  drops  of  ice. 

Q.  What  makes  ONE  bed  of  air  COLDER  than 
another  ? 


HAIL — RAIN.  313 

A.  It  is  frequently  caused  by  elec- 
tricity unequally  distributed  in  the  air. 

Q.       Why  is  HAIL  frequently  accompanied  with 

THUNDER  and  LIGHTNING? 

A.  1st — Because  the  congelation  of 
water  into  hail  disturbs  the  electricity  of 
the  air:  and 

2dly — The  friction  (produced  by  the 
fall  of  hail)  excites  it  still  more. 

Q.      Why  does  HAIL  fall  generally  in  SUMMER 

and  AUTUMN? 

A.  1st — Because  the  air  is  more 
highly  electrified  in  summer  and  autumn 
than  in  winter  and  spring1:  and 

2dly — The  vapors  in  summer  and 
autumn  (being*  rarefied)  ascend  to  more 
elevated  regions,  which  are  colder  than 
those  nearer  the  earth. 

Q.       What  TWO  things   are  essential  to  cause 

HAIL? 

A.  Two  strata  of  clouds  having-  oppo- 
site electricities,  and  two  currents  of  wind. 
The  lower  cloud  (being  negative)  is  the 
one  precipitated  in  hail. 

Q.       What  is  RAIN  ? 

A  The  vapor  of  the  clouds  or  air 
condensed,  and  precipitated  to  the  earth. 

Q.       When  is  the  vapor  of  the  air  or  clouds 
PRECIPITATED  in  hail,  rain,  or  snow  ? 
14 


314  RAIN. 

A.  When  the  air  is  saturated  with  va- 
por, and  a  cold  current  condenses  it ;  it 
is  then  no  longer  able  to  hold  all  its 
vapor  in  solution,  and  some  of  it  falls  as 
rain. 

Q.       Why  does  -RAIN  fall  in  DROPS  ? 

A.  Because  the  vapory  particles  in 
their  descent  attract  each  other ;  and 
those  which  are  sufficiently  near  unite, 
and  form  into  drops. 

Q.  Why  does  not  the  COLD  of  NIGHT  ALWAYS 
cause  rain  ? 

A.  Because  the  air  is  not  always  near 
saturation ;  and  unless  this  be  the  case, 
it  will  be  able  to  hold  its  vapor  in  solu- 
tion, even  after  it  is  condensed  by  the 
chilly  night. 

Q.  Why  does  a  PASSING  CLOUD  often  drop 
RAIN  ? 

A.  Because  the  cloud  (travelling 
about  on  the  wind)  comes  into  contact 
with  something  that  chills  it ;  and  its  va- 
por being  condensed,  falls  to  the  earth  as 
rain. 

Q.  Why  are  RAIN-DROPS  sometimes  much 
LARGER  than  at  OTHER  times  ? 

A.  Because  the  rain-cloud  is  floating 
near  the  earth;  when  this  is  the  case, 
the  drops  are  large,  because  such  a 


RAIN-WATER.  315 

cloud  is  much  more  dense  than  one  more 
elevated. 

The  size  of  the  rain-drop  is  also  increased,  according  to 
the  rapidity  with  which  the  vapors  are  condensed. 

Q.  Does  not  WIND  sometimes  INCREASE  the 
SIZE  of  ram-drops  ? 

A.  Yes ;  by  blowing1  two  or  more 
drops  into  one. 

Q.       Why  do  CLOUDS  FALL  in  RAINY  weather  ? 

A.  1st — Because  they  are  heavy  with 
abundant  vapor :  and 

2dly — The  density  of  the  air  being- 
diminished,  is  less  able  to  buoy  the  clouds 
up. 

Q.  How  do  you  KNOW  that  the  DENSITY  of  the 
air  is  DHMINISHED  in  RATNY  weather  ? 

A.  Because  the  mercury  of  a  ba- 
rometer falls. 

Q.  Why  is  RAIN-WATER  more  FERTILIZING 
than  PUMP-WATER  ? 

•A.  1st — Because  it  contains  more 
carbonic  acid :  and 

2dly — It  contains  also  a  small  quan- 
tity of  ammonia,  with  which  it  supplies 
the  young-  plants. 

It  is  probable  that  the  ammonia  of  rain-water  is  merely 
that  which  escapes  from  putrefying  animal  matters,  beaten 
back  by  the  force  of  the  shower. 

Q.       Why  does  RAIN  PURIFY  the  AIR  ? 

A.     1st — Because   it   beats  down  the 


316  RAIN. 

noxious  exhalations  collected  in  the  air, 
and  dissolves  them : 

2dly — It  mixes  the  air  of  the  upper 
regions  with  that  of  the  lower  regions: 
and 

3dly — It  washes  the  earth,  and  sets  in 
motion  the  stagnant  contents  of  sewers 
and  ditches. 

Q.  Why  are  MOUNTAINOUS  countries  more 
RAINY  than  flat  ones  ? 

A.  Because  the  air  (striking*  against 
the  sides  of  the  mountains)  is  carried  up 
the  inclined  plane,  and  brought  in  contact 
with  the  cold  air  of  the  higher  regions : 
in  consequence  of  which,  its  vapor  is 
condensed,  and  deposited  in  rain. 

Q.  Why  does  a  SPONGE  SWELL  when  it  is 
WETTED  ? 

A.  Because  the  water  penetrates  the 
pores  of  the  sponge  by  capillary  attrac- 
tion, and  drives  the  particles  farther  from 
each  other  ;  in  consequence  of  which,  the 
hulk  of  the  sponge  is  greatly  increased. 

Q.          Why    do    FIDDLE-STRINGS     SNAP    in    WET 

weather  ? 

A.  Because  the  moisture  of  the  air 
(penetrating  the  string)  causes  it  to 
swell;  and  (as  the  cord  thickens)  its 
tension  is  increased,  and  the  string  snaps. 


MOISTURE.  317 

Q.  Why  does  PAPER  PUCKER  when  it  is  WET- 
TED ? 

A.  Because  the  moisture  (penetrating* 
the  paper)  drives  its  particles  farther 
apart ;  and  (as  the  moisture  is  absorbed 
unequally  by  the  paper)  some  parts  are 
more  enlarged  than  others ;  in  conse- 
quence of  which,  the  paper  blisters  or 
puckers. 

Q.  Why  do  the  weather-toys  (called  CAPUCHINS) 
lift  the  cowl  over  the  figures  in  wet  weather,  and 
remove  it  in  dry  ? 

A.  Because  the  cowl  of  the  cap'uchin 
is  attached  to  a  piece  of  cat-gut  in  such  a 
manner,  that  when  the  cat-grit  is  short- 
ened by  moisture,  it  pulls  the  cowl  up ; 
but  in  dry  weather  the  string  is  loosened, 
and  the  cowl  falls  down  by  its  own 
weight. 

Q.  In  another  weather-toy  the  MAN  comes  out 
in  WET  weather,  and  the  LADY  in  FINE  : — Why  is 
this  ? 

A.  Because  the  two  figures  are  at- 
tached to  a  piece  of  cat-gut  in  such  a 
manner,  that  when  the  cat-gut  is  short- 
ened by  moisture,  it  pulls  the  man  out ; 
but  when  it  is  loose,  the  woman  falls  out 
by  her  own  weight. 

Q.  Why  are  WET  STOCKINGS  DIFFICULT  to 
PULL  ON  ? 


318  RAIN. 

A.  Because  the  moisture  penetrates 
the  threads  of  the  stockings,  and  causes 
them  to  shrink  in  size. 

Q.  In  which  PART  of  the  DAY  does  the  MOST 
-RAIN  fall  ? 

A.  More  rain  falls  by  night  than  by 
day ;  because  the  cold  night  condenses 
the  air,  and  diminishes  its  capacity  for 
holding  vapor  in  solution. 

Q.  Does  more  rain  fall  in  SUMMER  or  in  WIN- 
TER? 

A.  There  are  more  rainy  days  from 
September  to  March ;  but  heavier  rains 
between  March  and  September. 

Q.  Why  are  there  MORE  RAINY  DAYS  from 
September  to  March  than  from  March  to  September? 

A.  Because  the  temperature  of  the 
air  is  constantly  decreasing,  and  its  capa- 
city for  holding  vapor  decreases  also ; 
in  consequence  of  which,  it  is  frequently 
obliged  to  part  with  some  of  its  vapor 
in  rain. 

Q.       In  what  PART  of  the  WORLD  does  RAIN  fall 

MOST  ABUNDANTLY  ? 

A.  Near  the  equator  ;  and  the  quan- 
tity of  rain  decreases,  as  we  approach  the 

poles. 

Be  it  remembered  that  there  are  fewer  rainy  days, 
although  more  rain  actually  falls  during  the  wet  season 
of  the  equator,  than  falls  in  12  months  at  any  other  part 
of  the  globe. 


PUMP-WATER.  319 

WATER. 

CHAPTER  XXVII. 

Q.       Of  what  is  WATER  composed  ? 

A.  Of  two  gases,  oxygen  and  hydro- 
gen. 

In  91bs.  of  water — 8  are  oxygen,  and  1  is  hydrogen. 
Q.       Why  is  WATER  FLUID  ? 

A.  Because  its  particles  are  kept 
separate  by  latent  heat :  When  a  cer- 
tain quantity  of  this  latent  heat  is  driven 
out,  water  becomes  solid,  and  is  called 
ice. 

By  increasing  its  latent  heat,  the  particles  of  water  are 
again  subdivided  into  invisible  steam. 

Q.       Why  is  PUMP- WATER  called  "  HARD  water  ?" 

A.  Because  it  is  laden  with  foreign 
matters,  and  will  not  readily  dissolve 
substances  immersed  in  it. 

Q.       What  makes  PUMP-WATER  HARD  ? 

A.  When  it  filters  through  the  earth, 
it  becomes  impregnated  with  sulphate  of 
lime,  and  many  other  impurities  from  the 
earths  and  minerals  with  which  it  comes 
in  contact. 

Q.        What  is  the  cause  of  MINERAL  SPRINGS  ? 

A.  When  water  trickles  through  the 
ground,  it  dissolves  some  of  the  substan- 
ces with  which  it  comes  in  contact ;  if 


320  WATER. 

these  substances  are  metallic,  the  water 
will  partake  of  their  mineral  character. 

Some  water  is  imbued  with  lime ;  some  with  sail,  &c.,  &c. 

Q.  Why  is  it  difficult  to  WASH  our  HANDS 
clean  with  HARD  water  ? 

A.  Because  the  soda  of  the  soap  com- 
bines with  the  sulphuric  acid  of  the  hard 
water — and  the  oil  of  the  soap  with  the 
lime — and  floats  in  flakes  on  the  top  of 
the  water. 

N.  B.   Sulphate  of  lime  consists  of  sulphuric  acid  and 
lime. 

Q.       Why  is  it  difficult  to  wash  in  SALT  WATER  ? 

A.  Because  it  contains  muriatic  acid  ; 
and  the  soda  of  soap  combines  with  the 
muriatic  acid  of  the  salt  water,  and  pro- 
duces a  cloudiness. 

Q.       What  is  the  cause  of  PETRIFACTIONS  ? 

A.  While  water  rolls  underground, 
its  impurities  are  held  in  solution  by  the 
presence  of  carbonic  acid :  but  when 
the  stream  reaches  the  open  air,  its  car- 
bonic acid  escapes,  and  these  impurities 
are  precipitated  on  various  substances 
lying*  in  the  course  of  the  stream. 

These  impurities  are  especially  carbonate  of  lime  and 
iron. 

Q.  Why  does  a  BLACK  HAT  turn  RED  at  the 
SEA-SIDE  ? 

A.     Because  the  muriatic  acid  of  the 


SOAP — RAIN-WATER.  321 

sea  water  disturbs  the  gallic  acid  of  the 
black  dye,  and  turns  it  red. 

Q.       Of  what  is  SOAP  made  ? 

A.  Of  kelp  (or  the  ashes  of  sea- weed 
dried  and  burnt  in  a  pit)  mixed  with  oil 
or  fat. 

YELLOW  SOAP  is  made  of  whale  oil,  soda,  and  resin. 
SOFT  SOAP  is  made  of  oil  and  potash.  HARD  SOAP,  of  oil 
and  soda. 

Q.       Why  does  WATER  CLEAN  dirty  LINEN  ? 

A.  Because  it  dissolves  the  stains,  as 
it  would  dissolve  salt. 

Q.  Why  does  SOAP  greatly  INCREASE  the  cleans- 
ing power  of  water  ? 

A.  Because  many  stains  are  of  a 
greasy  nature  ;  and  soap  has  the  power 
of  uniting  with  greasy  matters,  and  ren- 
dering* them  soluble  in  water. 

Q.       Why  is  RAIN-WATER  SOFT  ? 

A.  Because  it  is  not  impregnated 
with  earths  and  minerals, 

Q.  WJiy  is  it  MORE  EASY  to  WASH  with  SOFT 
water,  than  with  HARD  ? 

A.  Because  soft  water  unites  freely 
with  soap,  and  dissolves  it ;  instead  of  de- 
composing* it,  as  hard  water  does. 

Q.  Why  do  WOOD  ASHES  make  HARD  water 
SOFT? 

A.  1st — Because  the  carbonic  acid 
of  wood  ashes  combines  with  the  sulphate 
14* 


322  WATER. 

of  lime  in  the  hard  water,  and  converts 
it  into  chalk  :  and 

2dly — Wood  ashes  convert  some  of 
the  soluble  salts  of  water  into  insoluble, 
and  throw  them  down  as  a  sediment ;  in 
consequence  of  which,  the  water  remains 
more  pure. 

Q.  Why  has  RAIN-WATER  such  an  UNPLEASANT 
SMELL,  when  it  is  collected  in  a  rain-water  tub  or 
tank  ? 

A.  Because  it  is  impregnated  with 
'decomposed  organic  matters,  washed 
from  roofs,  trees,  or  the  casks  in  which 
it  is  collected. 

Q.       Why  does  WATER  MELT  SUGAR  ? 

A.  Because  very  minute  particles  of 
water  insinuate  themselves  into  the 
pores  of  the  sugar,  by  capillary  attrac- 
tion ;  and  force  the  crystals  apart  from 
each  other. 

Q.       Why  does  WATER  MELT  SALT? 

A.  Because  very  minute  particles 
of  water  insinuate  themselves  into  the 
pores  of  the  salt,  by  capillary  attraction ; 
and  force  the  crystals  apart  from  each 
other. 

Q.  Why  does  melted  SUGAR  or  SALT  give  a 
PLAVOR  to  water  ? 

A.  Because  the  sugar  or  salt  (being 
disunited  into  very  minute  pieces)  floats 


SEA-WATER — STAGNANT    WATER.       323 

about  the  water,  and  mixes  with  every 
part. 

Q.  Why  does  HOT  water  melt  sugar  and  salt 
QUICKER  than  COLD  water  ? 

A.  Because  the  heat  (entering*  the 
pores  of  the  sugar  or  salt)  opens  a  pas- 
sage for  the  water. 

Q.       V^Hiy  is  SEA-WATER  brackish  ? 

A.  1st — Because  the  sea  contains 
mines  of  salt  at  the  bottom  of  its  bed  : 

2dly — It  is  impregnated  with  bitumi- 
nous matter,  which  is  brackish  :  and 

3dly — It  contains  many  putrid  sub- 
stances of  a  brackish  nature. 

Q.  Why  is  NOT  RAIN-WATER  SALT,  although 
most  of  it  is  evaporated  from  the  SEA  ? 

A.  Because  salt  will  not  evaporate; 
and  therefore  when  sea-water  is  turned 
into  vapor,  its  salt  is  left  behind. 

Q.       Why  does  STAGNANT  water  PUTREFY  ? 

A.  Because  leaves,  plants,  insects, 
&c.,  are  decomposed  in  it. 

Q.       Why  is  STAGNANT  water  full  of  WORMS, 

EELS,  <SfC.  ? 

A.  Because  numberless  insects  lay 
their  eggs  in  the  leaves  and  plants  float- 
ing on  the  surface ;  these  eggs  are  soon 
hatched,  and  produce  swarms  of  worms, 
eels,  and  insects. 


324  WATER. 

Q.  Why  is  FLOWING  water  FREE  from  these 
IMPURITIES  ? 

A.  1st — Because  the  motion  of  run- 
ning* water  prevents  fermentation  : 

2dly — It  dissolves  the  putrid  substan- 
ces which  happen  to  fall  into  it :  and 

3dly — It  casts  on  the  bank  (by  its 
current)  such  substances  as  it  cannot 
dissolve. 

Q.  Why  does  RUNNING  water  OSCILLATE  and 
WHIRL  in  its  current  ? 

A.  1st — Because  it  impinges  against 
its  banks,  and  is  perpetually  diverted 
from  its  forward  motion  :  and 

2dly — Because  the  centre  of  a  river 
flows  faster  than  its  sides. 

Q.  Why  do  the  SIDES  of  a  river  flow  more 
TARDILY  than  its  CENTRE  ? 

A.  Because  they  rub  against  the 
banks,  and  are  delayed  in  their  current 
by  this  friction. 

Q.       Why  does  SOAPY  water  BUBBLE  ? 

A.  Because  soap  makes  the  water  te- 
nacious ;  and  prevents  the  bubbles  from 
bursting  as  soon  as  they  are  formed. 

Q.       Why  will  not  water  bubble  WITHOUT  SOAP  ? 

A.  Because  it  is  not  tenacious  enough 
to  hold  together  the  bubbles  that  are 
formed. 


ICE.  325 

Q.       When  SOAP-BUBBLES  are  blown  from  a  pipe 
why  do  they  ASCEND  ? 

A.     Because  they  are  filled  with  warm 
breath,  which  is  lighter  than  air. 


ICE. 

CHAPTER  XXVIII. 

Q.       What  is  ICE  ? 

A.  FROZEN  WATER.  When  the  air 
is  reduced  to  32  degrees  of  heat,  water 
will  no  longer  remain  in  a  fluid  state. 

Q.       Why  is  SOLID  ICE  LIGHTER  than  WATER  ? 

A.  Because  water  expands  by  freez- 
ing ;  and  as  the  bulk  is  increased,  the 
gravity  must  be  less. 

Nine  cubic  inches  of  water  become  ten  when  frozen. 
Q.       Why  do  EWERS  BREAK  in  a  FROSTY  NIGHT  ? 
A.     Because  the  water  in  them  freez- 
es ;  and  (expanding  by  frost)  bursts  the 
ewers  to  make  room   for  its  increased 
volume. 

Q.  Why  does  it  not  expand  UPWARDS  (like 
boiling  water),  and  RUN  OVER  ? 

A.  Because  the  surface  is  frozen 
first ;  and  the  frozen  surface  acts  as  a 
plug,  which  is  more  difficult  to  burst 
than  the  earthen  ewer  itself. 


326  ICE. 

Q.  Why  do  TILES,  STONES,  and  ROCKS  often 
SPLIT  in  winter  ? 

A.  Because  the  moisture  in  them 
freezes  ;  and  (expanding-  by  frost)  splits 
the  solid  mass. 

Q.  In  winter-time,  FOOT-MARKS  and  WHEEL- 
RUTS  are,  often  covered  with  an  icy  NET-WORK, 
through  the  interstices  of  which  the  soil  is  clearly 
seen  : — WHY  does  the  water  freeze  in  NET-WORK? 

A.  Because  it  freezes  first  at  the 
sides  of  the  foot-prints :  other  crystals 
gradually  shoot  across,  and  would  cover 
the  whole  surface,  if  the  earth  did  not 
absorb  the  water  before  it  had  time  to 
freeze. 

Q.  In  winter-time,  these  FOOT-MARKS  and 
WHEEL-RUTS  are  sometimes  covered  with  a  perfect 
SHEET  of  ice,  and  not  an  icy  net-work: — Why  is 
THIS? 

A.  Because  the  air  is  colder  and  the 
earth  harder  than  in  the  former  case,  in 
consequence  of  which,  the  entire  surface 
of  the  foot-print  is  frozen  over  before  the 
earth  has  had  time  to  absorb  the  water. 

Q.  WJiy  is  not  the  ice  SOLID  in  these  ruts  ? — • 
WHY  is  there  only  a  very  thin  FILM  or  NET-WORK  of 

ice? 

A.  Because  the  earth  absorbs  most  of 
the  water,  and  leaves  only  the  icy  film 
behind. 


EXPANSION    OF    WATER. 


327 


Q.  Why  do  WATER-PIPES  frequently  BURST  in 
FROSTY  weather  ? 

A.  Because  the  water  in  them  freez- 
es ;  and  (expanding  by  frost)  bursts  the 
pipes  to  make  room  for  its  increased 
volume. 

Q.  Does  not  water  expand  by  HEAT  as  well  as 
by  COLD  ? 

A.  Yes ;  it  expands  as  soon  as  it  is 
more  than  42  degrees,  till  it  boils ;  after 
which  time,  it  flies  off  in  steam. 

Freezing  water,  32°.  212°,  Boiling  water. 


Here  A  B  measures  the  bulk  of  a  portion  of  water  at 
42  degrees. 

It  goes  on  increasing  in  bulk  to  C  D,  when  it  boils. 
It  also  goes  on  increasing  in  bulk  to  E  F,  when  it  freezes. 

Q.  WHEN  does  WATER  begin  to  EXPAND  from 
cold? 

A.  When  it  is  reduced  to  42  degrees. 
Water  is  wisely  ordained  by  God  to  be 
an  exception  to  a  very  g-eneral  rule — it 
contracts  till  it  is  reduced  to  42  degrees, 
and  then  it  expands  till  it  freezes. 

The  general  rule  is  this — That  cold  condenses  and  con- 
tracts the  volume  of  nearly  everything ;  but  water  is  not 
contracted  by  cold  after  it  freezes,  (which  it  does  at  32°). 


328  ICE. 

Q.      WHY  does  water  expand  when  it  freezes? 

A.  Because  it  is  converted  into  solid 
crystals  which  do  not  jit  so  closely  as  par- 
ticles of  water  do. 

Q.  Why  is  tJie  BOTTOM  of  a  river  NEVER  FRO- 
ZEN ? 

A.  Because  water  ascends  to  the 
surface,  so  soon  as  it  becomes  colder 
than  42  degrees ;  and  (if  it  freezes)  floats 
there  till  it  is  melted. 

Q.  Skow  the  WISDOM  of  GOD  in  this  wonderful 
exception  to  a  general  law. 

A.  If  ice  were  heavier  than  water,  it 
would  sink ;  and  a  river  would  soon  be- 
come a  solid  block  of  ice,  which  could 
never  be  dissolved. 

The  general  rule  is— that  all  substances  become  heavier 
from  condensation ;  but  ice  is  lighter  than  water. 

Q.  Why  does  not  the  ICE  on  the  SURFACE  of  a 
river  CHILL  the  water  BENEATH  and  make,  it  freeze1? 

A.  1st — Because  water  is  a  very  bad 
conductor,  and  is  heated  or  chilled  by 
CONVECTION  only  : 

2dly — If  the  ice  on  the  surface  were 
to  communicate  its  coldness  to  the  water 
beneath,  the  water  beneath  would  com- 
municate its  heat  to  the  ice,  and  the  ice 
would  instantly  mdt :  and 

3dly — The  ice  on  the  surface  acts  as 
a  shield,  to  prevent  the  cold  air  from 


FROZEN    RIVERS.  329 

penetrating  through  the  river,  to  freeze 
the  water  below  the  surface. 

Q.  Why  does  WATER.  FREEZE  at  the  SURFACE 
first  ? 

A.  Because  the  surface  is  in  contact 
with  the  air,  and  the  air  carries  away  its 
heat. 

Q.  Why  does  the  coat  of  ice  grow  THICKER  and 
THICKER  if  the  frost  CONTINUES  ?, 

A.  Because  the  heat  of  the  water 
(immediately  below  the  frozen  surface) 
passes  through  the  pores  of  the  ice  into 
the  cold  air. 

Q.  Why  are  not  WHOLE  RIVERS  FROZEN 
(layer  by  layer),  till  they  become  solid  ice  ? 

A.  Because  water  is  so  slow  a  con- 
ductor, that  our  frosts  never  continue 
long  enough  to  convert  a  whole  river  in- 
to a  solid  mass  of  ice. 

Q.  Why  does  not  RUNNING  water  freeze  so 
FAST  as  STILL  water? 

A.  1st — Because  the  motion  of  the 
current  disturbs  the  crystals,  and  prevents 
their  forming1  into  a  continuous  surface  : 
and 

2dly — The  heat  of  the  under  surface 
is  communicated  to  the  upper  surface  by 
the  rolling  of  the  water. 

Q.  When  RUNNING  wate?  is  FROZEN  why  is 
the  ICE  generally  very  ROUGH  ? 


330  ICE. 

A.  Because  little  flakes  of  ice  are 
first  formed  and  carried  down  the  stream, 
till  they  meet  some  obstacle  to  stop  them ; 
other  flakes  of  ice  (impinging-  against 
them)  are  arrested  in  like  manner ;  and 
the  edges  of  the  different  flakes  overlap- 
ping each  other,  make  the  surface  rough. 

Q.  Why  do  SOME  parts  of  a  RIVER  FREEZE 
LESS  than  OTHERS  ? 

A.  Because  springs  issue  from  the 
bottom ;  and  (as  they  bubble  upwards) 
thaw  the  ice,  or  make  it  thin. 

Q.  When  persons  FALL  into  a  RIVER  in  winter- 
time why  does  the  WATER  feel  remarkably  WARM? 

A.  Because  the  frosty  air  is  at  least 
10  or  12  degrees  colder  than  the  water  is. 

The  water  below  the  surface  is  at  least  42° ;  but  the 
air  32°,  or  even  less. 

Q.  Why  is  SHALLOW  water  FROZEN  more 
QUICKLY  than  DEEP  water  ? 

A.  Because  the  ivlwle  volume  of  water 
must  be  cooled  to  42  degrees,  before  the 
surface  can  be  frozen  :  and  it  takes  a 
longer  time  to  cool  down  a  deep  bed  of 
water  than  a  shallow  one. 

Q.       Why  is  SEA- WATER  RARELY  FROZEN? 

A.  1st — Because  the  mass  of  water 
is  so  great,  that  it  requires  a  very  long 
time  to  cool  the  whole  volume  down  to 
42  degrees : 


FREEZING.  331 

2dly — The  ebb  and  flow  of  the  sea  in- 
terfere with  the  cooling*  influence  of  the 
air  :  and 

3dly — Salt  water  never  freezes  till  the 
surface  is  cooled  down  25  degrees  below 
freezing  point. 

Q.  Why  do  some  LAKES  RARELY  (if  ever) 
FREEZE  ? 

A.  1st — Because  they  are  very  deep : 
and 

2dly — Because  their  water  is  supplied 
by  springs,  which  bubble  from  the  bot- 
tom. 

Q.       Why  does  the,  DEPTH  of  water  RETARD  its 

FREEZING  1 

A.  Because  the  whole  volume  of  water 
must  be  reduced  to  42  degrees,  before 
the  surface  will  freeze:  and  the  deeper 
the  water,  the  longer  it  will  be  before 
the  whole  volume  is  thus  reduced. 

Q.       Why  do  SPRINGS  at  the  bottom  of  a  lake 

PREVENT  its  FREEZING? 

A.  Because  they  keep  continually 
sending  forth  fresh  water,  which  pre- 
vents the  lake  from  being  reduced  to 
the  necessary  degree  of  coldness. 

Q.  It  is  COLDER  in  a  THAW,  than  in  a  FROST. 
Explain  the  reason  of  this. 

A.  When  frozen  water  is  thawed,  it 
absorbs  heat  from  the  air,  &c.,  to  melt 


332  ICE. 

the  ice ;  in  consequence  of  which,  the 
heat  of  the  air  is  greatly  reduced. 

Q.  It  is  WARMER  in  a  FROST  than  in  a  THAW. 
Explain  the  reason  of  this. 

A.  When  water  freezes,  it  gives  out 
latent  heat,  in  order  that  it  may  be  con- 
verted into  solid  ice ;  and,  as  much  heat 
is  liberated  from  the  water  to  the  atmos- 
phere, the  air  feels  warmer. 

Q.  SALT  DISSOLVES  ICE.  Explain  the,  reason 
of  this. 

A.  Water  freezes  at  32°,  but  salt 
and  water  will  not  freeze  till  the  air  is 
25  degrees  colder ;  if,  therefore,  salt  be 
added  to  frozen  water,  it  dissolves  it. 

Unless  the  thermometer  stands  below  7°. 
Q.       Will  any  thing  DISSOLVE  ICE  besides  SALT  ? 

A.  Yes  ;  any  acid,  such  as  sulphuric 
acid,  nitric  acid,  &c. 

Q.  Why  is  a  mixture  ^SALT  and  sxow  cold- 
er than  SNOW  itself? 

A.  Because  salt  dissolves  the  crystals 
of  snow  into  a  fluid  :  And  whenever  a 
solid  is  converted  into  a  fluid,  heat  is  ab- 
sorbed, and  the  cold  made  more  intense. 

Q.       Why  does  FROST  make  the  EARTH  CRACK  1 

A.     Because  the  water  absorbed  by 

the  earth  in  warm  weather,  expanding- 

by   the   frost,  thrusts   the  particles  of 


FROST.  333 

earth  apart  from  each  other,  and  leaves 
a  chink  or  crack  between. 

Q.  Show  the  WISDOM  of  GOD  in  this  arrange- 
ment. 

A.  These  cracks  in  the  earth  let  in 
air,  dew,  rain,  and  many  gases  favorable 
to  vegetation. 

Q.       Whfy  does  the  EARTH  CRUMBLE  in  SPRING  ? 

A.  Because  the  ice  of  the  clods  dis- 
solves; and  the  particles  of  earth  (which 
had  been  thrust  apart  by  the  frost)  being* 
left  unsupported,  tumble  into  minute  parts, 
because  their  cement  of  ice  is  dissolved. 

Q.  Why  does  MORTAR  CRUMBLE  away  in 
FROST? 

A.  Because  it  was  not  dried  in  the 
warm,  w&ather ;  therefore  its  moisture 
freezes,  expands,  and  thrusts  the  parti- 
cles of  the  mortar  away  from  each  other ; 
but  as  soon  as  the  frost  goes  the  water 
condenses,  and  leaves  the  mortar  full  of 
cracks  and  chinks. 

Q.  Why  does  STUCCO  PEEL  from  a  WALL  in 
FROSTY  weather  ? 

A.  Because  the  stucco  was  not  dried 
in  the  warm  weather ;  therefore  its  mois- 
tme  freezes,  expands,  and  thrusts  its  par- 
ticles away  from  the  wall ;  but,  as  soon 
as  the  water  condenses  again  by  the 

' 


334  ICE. 

thaw,   the  stucco  (being1  unsupported) 
falls  by  Us  own  weight. 

Q.  Why  cannot  BRICKLAYERS  and  PLASTERERS 
work  in  FROSTY  weather  ? 

A.  Because  frost  expands  mortar, 
and  causes  the  bricks  and  plaster  to 
start  from  their  position. 

Q.  Why  do  BRICKLAYERS  COVER  their  work 
with  STRAW  in  spring  and  autumn  ? 

A.  Because  straw  is  a  non-conduct- 
or; and  prevents  the  mortar  of  their 
new  work  from  freezing,  during-  the  cold 
nig*hts  of  spring1  and  autumn. 

Q.  Why  are  WATER  PIPES  often  covered  with 
STRAW  in  winter-time  ? 

A.  Because  straw  (being*  a  non-con- 
ductor) prevents  the  water  of  the  pipes 
from  freezing,  and  the  pipes  from  burst- 
ing. 

Q.  Why  are  delicate  TREES  covered  with  STRAW 
in  WINTER  ? 

A.  Because  straw  (being  a  non-con- 
ductor) prevents  the  sap  of  the  tree  from 
being*  frozen. 

Q.  Can  WATER  be,  FROZEN  in  any  way  BE- 
SIDES by  frosty  weather? 

A.  Yes;  in  very  many  ways.  For 
example — a  bottle  of  water  wrapped  in 
cotton,  and  frequently  wetted  ivit/i  ether, 
will  soon  freeze. 


FREEZING    MIXTURES.  335 

Q.  Why  would  WATER  FREEZE  if  the  bottle 
were  kept  constantly  wetted  with  ETHER  ? 

A.  Because  evaporation  would  carry 
off  the  heat  of  the  water,  and  reduce  it 
to  the  freezing  point. 

Q.  Why  does  ETHER  freeze  under  the  RECEIV- 
ER of  an  AIR-PUMP,  when  the  air  is  exhausted? 

A.  Because  evaporation  is  very 
greatly  increased  by  the  diminution  of 
atmospheric  pressure;  and  the  ether 
freezes  by  evaporation. 

FREEZING  MIXTURES. 

1.  If  nitre  be  dissolved  in  water,  the  heat  of  the  liquid 
will  be  reduced  16  degrees. 

2.  If  5  oz.  of  nitre,  and  5  of  sal-ammoniac  (both  finely 
powdered)  be  dissolved  in  19  oz.  of  water,  the  heat  of  the 
liquid  will  be  reduced  40  degrees. 

3.  If  81bs.  of  snow  be  added  to  lib.  of  salt,  the  mixture 
will  fall  to  0°  (or  32  degrees  below  freezing  point). 

The  two  following  are  the  coldest  mixtures  yet  known — 

1.  Mix  31bs.  of  muriate  of  lime  with  lib.  of  snow. 

2.  Mix  51bs.  of  diluted  sulphuric  acid  with  41bs.  of  snow. 

Q.  Why  is  it  more  easy  to  SWIM  in  the  SEA 
than  in  a  RIVER  ? 

A.  Because  the  specific  gravity  of 
salt  water  is  greater  than  that  of  fresh ; 
and,  therefore,  it  buoys  up  the  swimmer 
better. 

Q.  How  do  cooks  ascertain  if  their  BRINE  be 
SALT  ENOUGH  for  pickling  ? 

A.  They  put  an  egg  into  their  brine. 
If  the  eg-g*  sinks,  the  brine  is  not  strong 
enough  ;  if  the  egg-  floats,  it  is. 


336  SWIMMING. 

Q.  Why  will  an  EGG  SINK,  if  the  brine  be  NOT 
STRONG  enough  for  pickling  ? 

A.  Because  an  egg  will  be  the  hea- 
vier :  but  if  as  much  salt  be  added  as 
the  water  can  dissolve,  an  egg  will  be 
lighter  than  the  strong-  brine,  and  conse- 
quently float  on  the  surface. 

Q.  WHY  will  an  EGG  FLOAT  in  strong  BRINE 
and  not  in  water  ? 

A.  Because  the  specific  gravity  of 
salt  and  water  is  greater  than  that  of 
water  only. 

Q.  Why  do  persons  SINK  in  water  when  they 
are  UNSKILFUL  SWIMMERS? 

A.  Because  they  struggle  to  keep 
their  head  out  of  water. 

Q.      Explain  how  this  is. 

A.  When  the  head  is  thrown  back 
boldly  into  the  water,  the  mouth  is  kept 
above  the  surface,  and  the  swimmer  is 
able  to  breathe : 

But  when  the  head  is  kept  above  the 
surface  of  the  water,  the  chin  and  mouth 
sink  beneath  it,  and  the  swimmer  is  suf- 
focated. 

This  may  be  illustrated  thus : — If  a  piece  of  wood  be 
of  such  specific  gravity,  that  only  two  square  inches  can 
float  out  of  water ;  it  is  manifest,  that  if  two  other  inches 
are  raised  out,  the  too  former  inches  must  be  plunged  in. 
The  body  (in  floating)  resembles  this  piece  of  wood— 
If  two  square  inches  of  the  face  float  out  of  the  water,  the 
swimmer  can  breathe ;  but  if  part  of  the  back  and 


SWIMMING.  337 


of  the  head  be  forcibly  raised  above  the  surface,  a  propor- 
tional quantity  of  the  face  must  be  plunged  in;  and  the 
mouth  becomes  covered. 

Q.  Why  can  QUADRUPEDS  swim  MORE  EASILY 
than  MAN? 

A.  1st — Because  the  trunk  of  quad- 
rupeds is  lighter  than  water ;  and  this  is 
the  greatest  part  of  them  :  and 

2dly — The  position  of  a  beast  (when 
swimming-)  is  a  natural  one. 

Q.  Why  is  it  MORE  DIFFICULT  for  a  MAN  to 
swim  than  for  a  BEAST  ? 

A.  1st — Because  his  body  is  more 
heavy  in  proportion  than  that  of  a  beast : 
and 

2dly — The  position  and  muscular  ac- 
tion of  a  man  (when  swimming*)  differ 
greatly  from  his  ordinary  habits ;  but 
beasts  swim  in  their  ordinary  position. 

Q.  Why  can  FAT  men  SWIM  more  EASILY  than 
SPARE  men  ? 

A.  Because  fat  is  lighter  than  water  ; 
and  the  fatter  a  man  is,  the  more  bumf- 
ant  will  he  be. 

Q.  How  are  FISHES  able  to  ASCEND  to  the  SUR- 
FACE of  water  ? 

A.  Fishes  have  an  air-bladder  near 
the  abdomen ;  when  this  bladder  is 
filled  with  air  the  fish  increases  in  size, 
and  (being  lighter)  ascends  through  the 
water  to  its  surface. 
15 


338  LIGHT. 

Q.      How  are  fishes  able  to  DIVE  in  a  minute  to 
the  BOTTOM  of  a  stream  ? 

A.     They  expel  the  air  from  their  air-  i 
bladder ;  in  consequence  of  which,  their 
size  is  diminished,  and  they  sink  instant- 
ly. 


LIGHT. 

CHAPTER  XXIX. 

Q.       What  i»  LIGHT? 

A.  Rapid  undulations  of  a  fluid  called 
ether,  made  sensible  to  the  eye  by  strik- 
ing* on  the  optic  nerve. 

See  p.  51. 

Q.      How  FAST  does  LIGHT  TRAVEL  ? 

A.  Light  travels  so  fast,  that  it  would 
go  eight  times  round  the  earth  while  a 
person  counts  "  ONE." 

Q.      Does  ALL  light  travel  equally  fast  ? 

A.  Yes;  the  light  of  the  sun — the 
light  of  a  candle— or  the  light  from 
houses,  trees,  and  fields. 

Q.  Where  does  the  LIGHT  of  HOUSES,  TREES, 
and  FIELDS,  come  from  ? 

A.  The  light  of  the  sun  (or  of  some 
lamp  or  candle)  is  reflected  from  their 
surfaces. 


REFLECTION    OP    LIGHT.  339 

Q.  Why  are  SOME  surfaces  BRILLIANT  (like 
glass  and  steel),  and  OTHERS  DULL,  like  lead  ? 

A.  Those  surfaces  which  reflect  the 
most  light,  are  the  most  brilliant;  and 
those  which  absorb  light  are  dull. 

Q.       What  is  meant  by  REFLECTING  LIGHT? 

A.  Throwing  the  rays  of  li^ht  back 
again  from  the  surface  on  which  they 
fall. 

Q.       What  is  meant  by  ABSORBING  LIGHT  ? 

A.  Retaining  the  rays  of  light  on 
the  surface  on  which  they  fall ;  in  con- 
sequence of  which,  their  presence  is  not 
made  sensible  by  rejection. 

Q.  Why  can  a  THOUSAND  persons  SEE  the 
SAME  OBJECT  at  the  same  time  ? 

A.  Because  it  throws  off  from  its 
surface  an  infinite  number  of  rays  in 
all  directions ;  and  one  person  sees  one 
portion  of  these  rays,  and  another  person 
another. 

Q.       Why  is  the  EYE  PAINED  by  a  SUDDEN  light  ? 

A.  Because  the  nerve  of  the  eye  is 
burdened  ivith  rays  before  the  pupil  has 
had  time  to  contract. 

Q.  Why 'does  it  give  us  PAIN,  if  a  CANDLE  be 
brought  suddenly  towards  our  BED  at  night-time  ? 

A.  Because  the  pupil  of  the  eye  di- 
ites  very  much  in  the  dark,  in  order  to 
imit  more  rays.  When,  therefore,  a 


340  LIGHT. 

candle  is  brought  suddenly  before  us,  the 
enlarged  pupils  overload  the  optic  nerves 
unth  rays,  which  causes  pain. 

Q.  Why  CAN  we  BEAR,  the  candle-light  after  a 
few  moments  ? 

A.  Because  the  pupils  contract  again 
almost  instantly  ;  and  adjust  themselves 
to  the  quantity  of  light  which  falls  upon 
them. 

Q.  Why  can  we  SEE  NOTHING,  when  we  leave 
a  WELL-LIGHTED  room,  and  go  into  the  DARKER 

ROAD  Or  STREET  ? 

A.  Because  the  pupil  (which  con- 
tracted in  the  bright  room)  does  not  dilate 
instantaneously;  and  the  contracted  pu- 
pil is  not  able  to  collect  rays  enough 
from  the  darker  road  or  street  to  enable 
us  to  see  objects  before  us. 

Q.  Why  do  we  SEE  BETTER,  when  we  get.  USED 
to  the  DARK  ? 

A.  Because  the  pupil  dilates  again, 
and  allows  more  rays  to  pass  through 
its  aperture  ;  in  consequence  of  which, 
we  see  more  distinctly. 

Q.  If  we  look  at  the  SUN  for  a  few  moments, 
why  do  all  OTHER  things  appear  DAILK  ? 

A.  Because  the  pupil  of  the  eye  be- 
comes so  much  contracted  by  looking  at 
the  sun,  that  it  is  too  small  to  collect  suf- 
ficient rays  from  other  objects  to  enable 


VISION.  341 

us    to   distinguish    their   colors.      (See 
"  Accidental  colors  ;"  pp.  375,  376.) 

Q.  If  we  watch  a  bright  FIRE  for  a  few  moments^ 
why  does  the  ROOM  seem  DARK  ? 

A.  Because  the  pupil  of  the  eye  be- 
comes so  much  contracted  by  looking*  at 
the  fire,  that  it  is  too  small  to  collect  suf- 
ficient rays  from  the  objects  around  to 
enable  us  to  distinguish  their  colors. 

Q.  Why  can  we  see  the  PROPER  COLORS  of 
every  object  again,  after  a  few  minutes  ? 

A.  Because  the  pupil  dilates  again 
and  accommodates  itself  to  the  light 
around. 

Q.  Why  can  TIGERS,  CATS,  and  OWLS,  see  in 
the  DARK  ? 

A.  Because  they  have  the  power  of 
enlarging  the  pupil  of  their  eyes  so  as  to 
collect  several  scattered  rays  of  light ; 
in  consequence  of  which,  they  can  see 
distinctly  when  it  is  not  light  enough  for 
us  to  see  any  thing  at  all. 

Q.       Why  do  CATS  and  OWLS  SLEEP  almost  all 

DAY? 

A.  Because  the  pupil  of  their  eyes  is 
very  broad,  and  daylight  fatigues  them  ; 
so  they  close  their  eyes  for  relief. 

Q.  Why  do  CATS  keep  WINKING,  when  they  sit 
before  a  FIRE  ? 

A.     Because  the  pupil  of  their  eye  is 


342  LIGHT. 

very  broad,  and  the  light  of  the  fire  is 
painful ;  so  they  keep  shutting  their  eyes 
to  relieve  the  sensation  of  too  much  light. 

Q.  Why  do  TIGERS,  CATS,  OWLS,  <^e.,  PROWL 
by  NIGHT  for  prey  ? 

A.  Because  they  sleep  all  day  when 
the  strong  light  would  be  painful  to 
them  ;  and  as  they  can  see  clearly  in  the 
dark,  they  prowl  then  for  prey. 

Q.  Why  do  GLOW-WORMS  glisten  by  NIGHT 
only  ? 

A.  Because  the  light  of  day  is  so 
strong  that  it  eclipses  the  feeble  light  of 
a  glow-worm  ;  in  consequence  of  which, 
glow-worms  are  invisible  by  day. 

Q.  Wliy  can  we  NOT  see  the  STARS  in  the  DAY- 
TIME ? 

A.  Because  the  light  of  day  is  so 
powerful  that  it  eclipses  the  feeble  light  of 
the  stars :  in  consequence  of  which,  they 
are  invisible  by  day. 

Q.  Why  can  we  see  the  STARS  even  at  MID-DAY, 
from  the  bottom  of  a  deep  WELL  ? 

A.  Because  the  light  of  the  stars  is 
not  overpowered  by  the  rays  of  the  sun, 
which  are  lost  in  the  numerous  reflec- 
tions which  they  undergo  in  the  well. 

The  rays  of  the  sun  will  enter  the  well  very  obliquely: 
whereas,  many  stars  will  shine  directly  over  the  well.  See 
pp.  348,  349. 


THE    EYES.  343 


Q.  What  is  the  us^tf/*  TWO  EYES,  since  they 
present  only  one  image  of  any  object? 

A.  To  increase  the  light  —  or  to  take 
in  more  rays  of  light  from  the  object 
looked  at,  in  order  that  it  may  appear 
more  distinct. 

Q.  Why  do  we  NOT  see  things  DOUBLE,  with 
TWO  EYES? 

A.  1st  —  Because  the  axis  of  both  eyes 
is  turned  to  one  object;  and,  therefore, 
the  same  impression  is  made  on  the  ret'- 
ina  of  each  eye  :  and 

2dly  —  Because  the  nerves  (which  re- 
ceive the  impression)  have  one  point  of 
union  before  they  reach  the  brain. 

This  is  not  altogether  satisfactory,  although  it  is  the 
explanation  generally  given.  The  phenomenon  probably 
is  rather  psychological  than  material. 

Q.       Why  do  we  SEE  OURSELVES  in  a  GLASS  ? 

A.  Because  the  rays  of  light  from 
our  face  strike  against  the  surface  of  the 
glass,  and  (instead  of  being-  absorbed) 
are  reflected,  or  sent  back  again  to  our 
eye. 

Q.       Why  are  the  rays  of  light  REFLECTED  by 

a  MIRROR  1 

A.  Because  they  cannot  pass  through 
the  impenetrable  metal  with  which  the 
back  of  the  glass  is  covered;  so  they 
rebound  back,  just  as  a  marble  would  do, 
if  it  were  thrown  against  a  wall. 


344 


LIGHT. 


Q.       When  a  marble  is  rolled  towards  a  wall, 
what  is  tJie  path  THROUGH  WHICH  IT  RUNS  called  ? 

A.     The  line  of  INCIDENCE. 


Q.  When  a  marble  REBOUNDS  back  again, 
what  is  the  path  it  THEN  describes  called  ? 

A.     The  line  of  REFLECTION. 

See  figure  below.    If  AB  be  the  line  of  incidence,  then 
BC  is  the  line  of  reflection  ;  and  vice  versa. 

Q.  When  the  light  of  our  face  goes  TO  the 
GLASS,  what  is  the  path  through  which  it  goes 

CALLED? 

A.     The  line  of  incidence. 

Q.  When  the  light  of  our  face  is  reflected  BACK 
again  from  the  mirror,  what  is  this  RETURNING  path 
called  ? 

A.     The  line  of  reflection. 

Q.       What  is  the  ANGLE  of  incidence  ? 

A.  The  angle  between  the  line  of 
incidence  and  the  perpendicular. 

Q.       What  is  the  ANGLE  of  reflection  ? 

A.  The  angle  between  the  line  of 
reflection  and  the  perpendicular.  (See 
Fig.) 


REFLECTION. 


345 


Let  SS  be  any  surface,  PB  a  perpendicular  to  it. — If  a 
marble  were  thrown  from  A  to  B,  and  bounded  back  to 
C  ;  then  ABP  would  be  called  the  angle  of  incidence,  and 
CBP  the  angle  of  reflection. 

Q.  Why  does  our  reflection  in  a  mirror  seem 
to  APPROACH  us,  as  we  walk  TOWARDS  it ;  and  to 
RETIRE  FROM  us,  as  WE  retire  ? 

A.  Because  the  lines  and  angles  of 
incidence  are  always  equal  to  the  lines 
and  angles  of  reflection  ;  in  consequence 
of  which,  the  image  will  always  seem 
to  be  as  far  behind  the  mirror  as*  the  real 
object  is  before  it. 


Suppose  A  to  be  a  mirror— CA,  EA  and  DA,  FA,  the 
lines  of  incidence ;  then  GA,  KA  and  HA,  LA,  are  the 
lines  of  reflection.  When  the  arrow  is  at  CD,  its  image 
will  appear  at  GH,  because  line  CA=GA,  and  line  DA= 
HA;  and  also  the  angle  CAB=:angle  GAB,  and  angle 
DAB=HAB.  For  a  similar  reason,  if  the  arrow  were  at 
EF,  the  image  would  seem  to  be  at  KL. 

Q.       Why  can  a  man  see  his  WHOLE  PERSON 
reflected  in  a  LITTLE  MIRROR,  not  6  inches  in  length  ? 

A.     Because  the  lines  and  angles  of 

incidence  are  always  equal  to  the  lines 

and  angles  of  reflection ;  in  consequence 

of  which,  his  image  will  seem  to  be  as 

15* 


346  LIGHT. 

far  behind  the  mirror  as  his  person  is 
before  it. 

Take  the  last  figure — CD  is  much  larger  than  the  mir- 
ror A  ;  but  the  head  of  the  arrow  C  is  reflected  obliquely 
behind  the  mirror  to  G ;  and  the  barb  D  appears  at  H. — 
Why  1  Because  line  CA=GA,  and  line  DA=:HA ;  also  the 
angle  CAB=angle  GAB,  and  angle  DAB=HAB. 

Q.  Why  does  the  IMAGE  of  any  object  in  WA- 
TER always  appear  INVERTED  ? 

A.  Because  the  angles  of  incidence 
are  always  equal  to  the  angles  of  reflec- 
tim. 


Here  the  arrow-head  A  strikes  the  water  at  F,  and  is 
reflected  to  D ;  and  the  barb  B  strikes  the  water  at  E,  and 
is  reflected  to  C. 

If  a  spectator  stands  at  G,  he  will  see  the  reflected  lines 
CE  and  DF  produced  as  far  as  G. 

It  is  very  plain,  that  A  (the  more  elevated  object)  will 
strike  the  water,  and  be  projected  from  it  more  perpen- 
dicularly than  the  point  B ;  and,  therefore,  the  image  will 
seem  inverted.  See  p.  345. 

Q.       When  we  see  our  REFLECTION  in  WATER, 
why  do  we  seem  to  STAND  on  our  HEAD  ? 

A.     Because  the  angles  of  incidence 


GLASS    AS    A    REFLECTOR. 


347 


are  always  equal  to  the  angles  of  reflec- 
tion. 

Suppose  our  head  to  be  at  A,  and  our  feet  at  B  ;  then 
the  shadow  of  our  head  will  be  seen  at  D,  and  the  shadow 
of  our  feet  at  C.  (See  figure  on  p.  346.) 

Q.  Why  do  WINDOWS  seem  to  BLAZE  at  SUN- 
RISE and  SUN-SET  ? 

A.  Because  glass  is  a  good  reflector 
of  light ;  and  the  rays  of  the  sun  (strik- 
ing against  the  window-glass)  are  re- 
fleeted,  or  thrown  back. 

Q.  Why  do  NOT  windows  reflect  the  NOON-DAY 
rays  also  ? 

A.  They  do,  but  the  reflection  is  not 
seen.  ' 

Q.  Why  is  the  reflection  of  the  RISING  and 
SETTING  sun  seen  in  the  window,  and  NOT  that  of 
the  NOON-DAY  sun  ? 

A.  Because  the  rays  of  the  noon-day 
sun  enter  the  glass  too  obliquely  for  their 
reflection  to  be  seen. 

Sun  near  noon. 
At 


Sun  near  the  horizon. 


348 


LIGHT. 


In  the  preceding  cut,  AB  represents  a  ray  of  the  noon* 
day  sun  striking  the  window  at  B  ;  its  reflection  will  be  at  C. 

But  DB  (a  ray  of  the  rising  or  setting  sun)  will  be  re- 
flected to  E  (the  eye  of  the  spectator.) 

Q.  Why  can  we  not  see  the  REFLECTION  of  the 
SUN  in  a  WELL,  during  the  day-time  ? 

A.  Because  the  rays  of  the  SUN  fall 
so  obliquely  that  they  never  reach  the 
surface  of  the  water  at  all,  but  strike 
against  the  brick  sides. 

THE  SUN. 


Let  BDEC  be  the  well,  and  DE  the  water . 

The  ray  AB  strikes  against  the  brick-work  inside  the 
wall;  and 

The  ray  AC  strikes  against  the  brick-work  outside  the 
well. 

None  will  ever  touch  the  water  DE. 

Q.  Why  are  STARS  REFLECTED  in  a  WELL 
although  the  su^  is  NOT  ? 

A.  Because  the  rays  of  those  STARS, 
which  pass  nearly  over-head,  will  not  fall 


REFLECTION    ON    WATER. 


349 


so  obliquely  into  the  well  as  the  rays  of 
the  sun. 


THE  MOON  OR  A  STAR. 
A 


Here  the  star's  rays  AB,  AC,  botli  strike  the  water  DE, 
and  are  reflected  by  it. 

Q.  On  a  lake  of  water,  the  MOON  seems  to  make 
a  PATH  of  light  towards  the  eye  of  the  spectator,  while 
all  the  REST  of  the  lake  seems  DARK — WHY  is  this  ? 

A.     Because  the  lake  is  in  deep  sha-  . 
dow  /  and  many  rays  which  would  be 
eclipsed  by  the  broad  light  of  day  be- 
come visible. 

The  same  path  of  light  may  be  discerned  in  the  day-time, 
when  a  cloud  passes  over  the  sun. 

Q.  In  a  sheet  of  water  at  noon,  the  sun  appears 
to  shine  upon  only  ONE  spot,  and  all  the  REST  of  the 
water  seems  DARK — WHY  is  this  ? 

A.  Because  the  rays  fall  at  various 
degrees  of  obliquity  on  the  water,  and 


350 


LIGHT. 


are  reflected  at  similar  angles ;  but  as 
only  those   which   meet  the  eye  of  the 
spectator  are  visible,  all  the  water  wil 
appear  dark  except  that  one  spot. 


Here,  of  the  rays  SA,  SB,  and  SC,  only  the  ray  SO 
meets  the  eye  of  the  spectator  D. 

The  spot  0,  therefore,  will  appear  luminous  to  the  spec- 
tator D,  but  no  other  spot  of  the  water  ABC. 

Q  ~[\Hiy  are  MORE  STARS  visible  from  a  MOUN- 
TAIN than  from  a  PLAIN  1 

A.  Because  they  have  less  air  to  pass 
through.  As  air  absorbs  and  diminishes 
light ;  therefore,  the  higher  we  ascend, 
the  less  light  will  be  absorbed. 

Q.  Why  do  the  SUN  and  MOON  seem  LARGER. 
at  their  RISING  and  SETTING,  than  at  any  other 
time  ?  . 

A.  Because  the  arch  of  the  sky  (in 
which  the  sun  and  moon  are  seen)  is 


SUN    AT    HORIZON. 


351 


further  distant  at  the  horizon  than  it  is 
over-head. 


Let  MM  be  the  orbit  of  the  sun  or  moon. 

Let  BD  be  the  arch  of  the  sky,  in  which  the  sun  and 
moon  are  seen  by  us. 

It  will  be  seen  from  the  figure,  that  the  sun  or  moon  at 
the  horizon  will  appear  much  larger,  because  CD  is  longer 
than  CB. 

The  Phenomenon  referred  to  on  p.  350,  (called  the  hor- 
izontal Sun  and  Moon),  has  perplexed  philosophers  to  the 
present  hour.  The  solution  given  is  not  altogether  satis- 
factory—Sir J.  Herschell  says,  "  The  dilated  size  of  the 
sun  or  moon,  when  seen  near  the  horizon,  has  nothing  to 
do  with  refraction.  It  is  an  illusion  of  the  judgment,  aris- 
ing from  the  terrestrial  objects  interposed,  or  placed  in 
comparison  with  them.  Actual  measurement  with  a  pro- 
per instrument  corrects  our  error,  without,  however,  dis- 
pelling our  illusion — the  whole  is  owing  to  the  effect  of 
parallax." 


352  LIGHT. 

Q.  Why  can  we  NOT  SEE  into  tJie  STREET  or 
road,  when  CANDLES  are  LIGHTED  ? 

A.  1st — Because  glass  is  a  reflector, 
and  throws  the  candle-light  back  into  the 
room  again  :  and 

2dly — -The  pupil  of  the  eye  (having 
become  contracted  by  the  light  of  the 
room)  is  too  small  to  collect  rays  enough 
from  the  dark  street  to  enable  us  to  see 
into  it. 

Q.  Why  do  we  often  see  the  FIRE  REFLECTED 
in  our  parlor  WINDOW  in  winter-time  ? 

A.  Because  glass  is  a  good  reflector ; 
and  the  rays  of  the  fire  (striking  against 
the  window-glass)  are  reflected  back  into 
the  room  again. 

Q.  Why  do  we  often  see  the  image  of  our  CAN- 
DLES in  the  window,  while  we  are  sitting  in  our 
parlor  ? 

A.  Because  the  rays  of  the  candle 
(striking  against  the  glass)  are  reflected 
back  into  the  room ;  and  the  darker  the 
night,  the  clearer  the  reflection. 

Q.  WHY  is  this  reflection  more  clear,  if  the 
external  AIR  be  DARK  ? 

A.  Because  the:  reflection  is  not 
eclipsed  by  the  brighter  rays  of  the  sun 
striking  on  tfie  other  side  of  the  window. 

Q.  If  the  SHADOW  of  an  object  be  thrown  on  a 
wall — the  CLOSER  the  object  is  held  to  the  CANDLE, 
the  LARGER  will  be  its  SHADOW.  Why  is  this  ? 


EFFECTS    OF    DISTANCE.  353 

A.  Because  the  rays  of  light  diverge 
(from  the  flame  of  a  candle)  in  straight 
lines  like  lines  drawn  from  the  centre  of 
a  circle. 


&\ 


-3 


Here  the  arrow  A  held  close  to  the  candle,  will  cast  the 
shadow  BF  on  a  wall ;  while  the  same  arrow  held  at  C 
would  cast  only  the  little  shadow  DE. 

Q.  When  we  enter  a  long  AVENUE  of  TREES, 
WHY  does  the  avenue  seem  to  get  NARROWER  and 
narrower  till  the  two  sides  appear  to  MEET  ? 

A.  Because  the  further  the  trees  are 
off,  the  more  acute  will  be  the  angle  that 
any  opposite  two  make  with  our  eye. 

^_<i>   ,g> 


Here  the  width  between  the  trees  A  and  B  will  seem  to 
be  as  great  as  the  line  AB : 


354  LIGHT. 

But  the  width  between  the  trees  C  and  D  will  seem  to 
be  no  more  than  EF. 

Q.  In  a  long,  straight  STREET,  WHY  do  the 
houses  on  the  opposite  sides  seem  to  APPROACH  NEARER 
together  as  they  are  more  DISTANT  ? 

A.  Because  the  more  distant  the 
houses  are  the  more  acute  will  be  the  an- 
gle which  any  opposite  two  make  with 
our  eye. 

Thus  in  the  last  figure, 

If  A  and  B  were  two  houses  at  the  'top  of  the  street,  the 
street  would  seem  to  be  as  wide  as  the  line  AB  : 

And  if  C  and  D  were  two  houses  at  the  bottom  of  the 
street,  the  street  there  would  seem  to  be  no  wider  than 
EF. 

Q.  In  an  AVENUE,  WHY  do  the  TREES  seem  to 
be  SMALLER  as  their  distance  increases  ? 

A.  Because  the  farther  tke  trees  are 
off,  the  more  acute  will  be  the  angle  made 
by  their  perpendicular  height  with  our 
eye. 


- 

Here  the  first  tree  AB  will  appear  the  height  of  the 
line  AB  ;  but  the  last  tree  CD  will  appear  only  as  high  as 
the  line  EF. 

Q.  In  a  long,  straight  STREET,  WHY  do  the 
houses  seem  to  be  SMALLER  and  smaller,  the  FURTHER 
they  are  OFF  ? 

A.  Because  the  further  any  house  is 
off,  the  more  acute  will  be  the  angle  made 
by  its  perpendicular  height  with  our  eye. 


PERPENDICULAR    HEIGHT. 


355 


Thus  in  the  last  figure, 

If  AB  be  a  house  at  the  top  of  the  street,  its  perpendic- 
ular height  will  be  that  of  the  line  AB. 

If  CD  be  a  house  at  the  bottom  of  the  street,  its  perpen- 
dicular height  will  appear  to  be  that  of  EF. 

Q.  Why  does  a  man  on  the  TOP  of  a  MOUN- 
TAIN, or  church  spire,  seem  to  be  no  BIGGER  than  a 
CROW? 

A.  Because  the  angle  made  in  our 
eye  by  the  perpendicular  height  of  the 
man  at  that  distance,  is  no  bigger  than 
that  made  by  a  crow  close  by. 


Let  AB  be  a  man  on  a  distant  mountain,  or  spire,  and 
CD  a  crow  close  by : 

The  man  will  appear  only  as  high  as  the  line  CD,  which 
is  the  height  of  the  crow. 

Q.  Why  does  the  MOON  appear  to  us  so  much 
LARGER  than  the  STARS,  though,  in  fact,  it  is  a  great 
deal  SMALLER  ? 

A.  Because  the  moon  is  very  much 
nearer  to  us  than  any  of  the  stars. 


356  LIGHT. 

Let  AB  represent  a  fixed  star,  and  CD  the  moon. 

AB,  though  much  the  larger  body,  will  appear  no  big- 
ger  than  EF  ;  whereas  the  moon  (CD)  will  appear  as  large 
as  the  line  CD  to  the  spectator  G. 

The  moon  is  240.000  miles  from  the  earth,  not  quite  a 
quarter  of  a  million  of  miles.  The  nearest  fixed  stars  are 
20.000,000,000,000.  (i.  e.,  20  billions.) 

If  a  ball  went  500  miles  an  hour,  it  would  reach  the 
moon  in  twenty  days :  but  it  would  not  reach  the  nearest 
fixed  star  in  4,500,000  years.  Had  it  begun,  therefore, 
when  Adam  was  created,  it  would  be  no  further  on  its 
journey  than  a  coach  (which  has  to  go  from  the  Land's 
End,  Cornwall,  to  the  most  northern  parts  of  Scotland) 
after  it  has  passed  about  three-quarters  of  a  mile. 

Q.  Why  does  the  MOON  (which  is  a  sphere) 
APPEAR  to  be  a  FLAT  surface  ? 

A.  Because  it  is  so  far  off  that  we 
cannot  distinguish  any  difference  be- 
tween the  length  of  the  rays  issuing*  from 
the  edge  and  those  which  issue  from  the 
centre. 


The  rays  AD  and  CD  appear  to  be  no  longer  than  the 
ray  BD  ;  but  if  all  the  rays  seem  of  the  same  length,  the 
part  B  will  not  seem  to  be  nearer  to  us  than  A  and  C  ;  and 
therefore  ABC  will  look  like  a  flat  or  straight  line. 

The  rays  AD  and  CD  are  240.000  miles  long. 

The  ray  BD  is  238,910  miles  long. 

Q.  Why  do  the  SUN  and  STARS  (which  are 
spheres)  appear  to  be  FLAT  surfaces  ? 

A.  Because  they  are  such  an  im- 
mense way  off,  that  we  can  discern  no 
difference  of  length  between  the  rays 
which  issue  from  the  edge  and  those 


TELESCOPES.  357 

which  issue  from  the  centre  of  these  bo- 
dies. 

The  rays  AD  and  CD  appear  no  longer  than  BD ;  and 
as  B  appears  to  be  no  nearer  than  A  or  C,  therefore  A,  B, 
C,  must  all  seem  equally  distant;  and  ABC  will  seem  a 
fiat  or  straight  line.  (See  last  figure,  p.  356.) 

Q.  Why  does  DISTANCE  make  an  object  IN- 
VISIBLE ? 

A.  Because  no  visible  perpendicular 
can  be  inserted  between  the  lines  which 
form  the  angle ;  or  because  the  lines 
actually  cross  before  they  meet  our  eye. 


??r 


Here  the  tree  AD  would  not  be  visible  to  the  spectator  C, 
even  if  he  were  to  approach  as  far  as  B ;  because  no  visi- 
ble perpendicular  can  be  inserted  between  the  two  lines 
AC,  DC,  at  the  point  B,  and  after  B  the  lines  would  cross : 
Therefore,  the  tree  would  be  invisible  from  C,  till  after  the 
spectator  had  passed  B. 

Q.  Why  do  TELESCOPES  enable  us  to  SEE 
objects  INVISIBLE  to  the  naked  eye? 

A.  Because  they  gather  tog-ether 
more  luminous  rays  from  obscure  objects 
than  the  eye  can ;  and  form  a  bright 
image  of  them  in  the  tube  of  the  tele- 
scope where  they  are  magnified. 

As  many  times  as  the  dimensions  of  the  object-glass  ex- 
ceed the  dimensions  of  the  pupil  of  the  eye,  so  many  times 
the  penetrating  powers  of  the  telescope  will  exceed  that 
of  the  naked  eye. 


358 


LIGHT. 


Q.  When  a  SHIP  (out  at  sea)  is  approaching 
the  shore,  why  do  we  SEE  the  small  MASTS  before  we 
see  the  bulky  HULL  ? 

A.  Because  the  earth  is  round  ;  and 
the  curve  of  the  sea  hides  the  hull  from 
our  eyes  after  the  tall  masts  have  become 
visible. 


Here,  only  that  part  of  the  ship  above  the  line  AG  can 
be  seen  by  the  spectator  A ;  the  rest  of  the  ship  is  hidden 
by  the  swell  of  the  curve  DE. 

Q.        What  is  meant  by  REFRACTION  ? 

A.  Bending  a  ray  of  light,  as  it  passes 
from  one  medium  to  another. 

Q.  How  is  a  ray  of  light  BENT,  as  it  passes 
from  one  medium  to  another  ? 

A.  When  a  ray  of  light  passes  into  a 
denser  medium  it  is  bent  towards  the  per- 
pendicular. When  it  passes  into  a  rarer 
medium  it  is  bent  from  the  perpendicular. 


RIVERS.  359 

Suppose  DE  to  be  a  perpendicular  line. 

If  AB  (a  ray  of  light)  enters  the  water,  it  will  be  bent 
towards  the  perpendicular  to  C. 

If  (on  the  other  hand)  CB  (a  ray  of  light)  emerges 
from  the  water,  it  would  be  bent  away  from  the  perpen- 
dicular towards  A. 

Q.  Why  does  a  SPOON  (in  a  glass  of  water) 
always  appear  BENT  ? 

A.  Because  the  light  (reflected  from 
the  spoon)  is  refracted  as  it  emerges  from 
the  water. 

See  Fig.  2,  p.  358.  The  spoon  ABC  will  appear  bent,  like 
ABD. 

Q.  Why  does  a  river  always  appear  more 
shallow  than  it  really  is  ? 

A.  Because  the  light  of  the  bottom 
of  the  river  is  REFRACTED,  as  it  emerges 
out  of  the  water. 

See  Fig.  2,  p.  358.  The  bottom  of  the  river  will  appear 
elevated  like  the  bowl  of  the  spoon  D. 

Q.  How  much  deeper  is  a  river  than  it  seems 
to  be? 

A.  About  one-third.  If,  therefore,  a 
river  seems  only  4  feet  deep,  it  is  really 
6  feet  deep. 

The  exact  apparent  depth  would  be  4J.  To  find  the 
real  depth,  multiply  by  4  and  divide  by  3 — thus  4£X4-*-3 
=6,  real  depth. 

N.  B.  Many  boys  get  out  of  their  depth  in  bathing,  in 
consequence  of  this  deception.  Remember,  a  river  is  al- 
ways one-third  deeper  than  it  appears  to  be : — thus,  if  a 
river  seems  to  be  4  feet  deep,  it  is  in  reality  nearly  6  feet 
deep,  and  so  on. 

Q.  Why  do  fishes  seem  to  be  nearer  the  surface 
of  a  river  than  they  really  are  ? 


360  LIGHT. 

A.  Because  the  rays  of  light  from 
the  fish  are  refracted,  as  they  emerge  from 
the  eye :  and  (as  a  bent  stick  is  not  so 
far  from  end  to  end,  as  a  straight  one) 
so  the  fishes  appear  nearer  to  our  eye 
than  they  really  are. 

See  Fig.  2,  p.  358. 
Q.       Why  are  some  persons  NEAR-SIGHTED  ? 

A.  Because  the  COR'NEA  of  their  eye 
is  so  prominent,  that  the  image  of  distant 
objects  is  formed  before  it  reaches  the 
RET'INA  ;  and,  therefore,  is  not  distinctly 
seen. 

Q.       What  is   meant   by  the  "  COR'NEA  of  the 

EYE?" 

A.  All  the  outside  of  the  visible  part 
of  the  eye-ball. 

The  curve  ABC  is  called  the  COR 

NBA. 

If  this  curve   be    too  prominen 
(or  convex),  the  eye  is  near-sighted 

If  too  flat  (or  concave),  the  eye 
far-sighted. 

Q.  What  is  meant  by  the  "  RET'INA  of  th 
EYE?" 

A.  The  net-work,  which  lines  th 
back  of  the  eye,  is  called  the  ret'ina. 

The  net-work  ABC  is  called  the  ret 
ina,  and  the  projecting  part  DBF  is  calle 
the  cor'nea. 

))D  N.  B.  This  net-work  is  composed  o 
a  spreading  out  of  the  fibres  of  th 
nerve  of  vision. 


SPECTACLES.  361 

Q.  What  sort  of  GLASSES  do  NEAR-SIGHTED 
persons  wear  ? 

A.  If  the  cornea  be  too  convex  (or 
projecting1),  the  person  must  wear  double 
concave  glasses,  to  counteract  it. 

Q.       What  is   meant  by    "DOUBLE    CONCAVE 

GLASSES?" 

A.     Glasses  hollowed-in  on  both  sides. 

,  \  /        The  figure  A  is  double  concave,  or  concave  on 
•  1  \    both  sides. 

Q.  Where  is  the  IMAGE  of  objects  formed^  if 
the  cornea  be  too  convex  ? 

A.  If  the  cor'nea  be  too  convex ',  the 
image  of  a  distant  object  is  formed  in 
the  vitreous  humors  of  the  eye,  and  not 
on  the  retina. 


Thus  the  image  is  formed  at  DB, 
and  not  on  ABC  (the  retina). 


Q.  What  is  the  use  of  DOUBLE  CONVEX  SPEC 
TACLE  glasses  ? 

A.  To  cast  the  image  farther  backf 
in  order  that  it  may  be  thrown  upon  the 
ret'ina  and  become  visible. 

Q.       Why  are  OLD  people  FAR-SIGHTED  ? 

A.  Because  the  humors  of  their  eyes 
are  dried  up  by  age ;  in  consequence  of 
16 


362  LIGHT. 

which,  the  COR'NEA  sinks  in,  or  becomes 
flattened. 

Q.  Why  does  the  FLATTENING  of  the  COR'NEA 
prevent  persons  seeing  objects  which  are  NEAR  ? 

A.  Because  the  cor'nea  is  too  flat, 
and  the  image  of  near  objects  is  not 
completely  formed,  when  their  rays  reach 
the  RET'INA  ;  in  consequence  of  which, 
the  image  is  imperfect  and  confused. 


The  perfect  image  is  made  at  DE  j 
and  not  on  ABC  (the  retina). 


Q.       What  sort  of  GLASSES  do  OLD  people  WEAR  ? 

A.  As  their  cor'nea  is  not  sufficiently 
convex,  they  must  use  double  convex 
glasses,  to  enable  them  to  see  objects 
near  at  hand. 

Q.       What  sort  of  glasses  are  "  DOUBLE  CONVEX 

SPECTACLE-GLASSES  ?" 

A.  Glasses  which  curve  outwards  on 
both  sides. 


The  figure  A  is  double  convex,  or  convex  on  both 
sides. 


Q.       What  is  the  use  of  DOUBLE  CONVEX  spec- 
tacle-glasses ? 

A.     To  shorten  the  focus  of  the  eye. 


SIGHT.  363 

and  bring-  the  image  of  distant  objects 
upon  the  ret'ina. 

Q.  Why  do  NEAR-SIGHTED  persons  bring  objects 
CLOSE  to  the  eye,  in  order  to  SEE  THEM  ? 

A.  Because  the  distance  between 
the  front  and  back  of  the  eye  is  so  great, 
that  the  image  of  distant  objects  is  form- 
ed in  front  of  the  ret'ina  ;  but  when  ob- 
jects are  brought  near  to  the  eye,  their 
image  is  thrown  further  back,  and  made 
to  fall  on  the  ret'ina. 

Q.  Why  do  OLD  people  HOLD  objects  FAR  OFF, 
in  order  to  see  them  better  ? 

A.  Because  the  distance  between 
the  front  and  back  of  tJieir  eyes  is  not 
great  enough :  when,  however,  objects 
are  held  further  off,  it  compensates  for 
this  defect ;  and  a  perfect  image  is  form- 
ed on  the  ret'ina. 

Q.  Why  are  HAWKS  able  to  see  such  an  IM- 
MENSE way  off? 

A.  Because  they  have  a  muscle  in 
the  eye  which  enables  them  to  flatten 
their  cornea,  by  drawing  back  the  crys- 
talline lens.  See  p.  362. 

This  muscle  is  called  the  Marsnpium. 
Q.        Why  can  HAWKS  see  objects  within  half-a7i- 
inch  of  their  eye^  as  well  as  those  a  long  way  off? 

A.  Because  their  eyes  are  furnished 
with  a  flexible  bony  rim,  which  throws 


364  LIGHT. 

the  cor'nea  foncard,  and  makes  the  hawk 
near-sighted.  See  p.  360. 

Q.  Into  how  many  PARTS  may  a  RAY  of  LIGHT 
be  DIVIDED  ? 

A.  Into  three  parts  :  BLUE,  YELLOW, 
and  RED. 

N.  B.  These  three  colors,  by  combination,  make  seven. 
1. — RED.  2. — ORANGE  (or  red  and  yellow).  3. — YELLOW. 
4. — GREEN  (or  yellow  and  blue).  5. — BLUE.  6. — INDIGO 
(a  shade  of  blue) ;  and  7. — VIOLET  (or  blue  and  red). 

Q.  How  is  it  known,  that  a  ray  of  light  con- 
sists of  several  different  colors  ? 

A.  Because,  if  a  ray  of  light  be  cast 
upon  a  triangular  piece  of  glass  (called  a 
prism),  it  will  be  distinctly  divided  into 
seven  colors:  1. — Red;  2. — Orange; 
3._ Yellow  ;  4.— Green  ;  5.—.  Blue ; 
6. — Indigo ;  and  7. — Violet. 

Q.  Why  does  a  PRISM  DIVIDE  a  ray  of  light 
into  VARIOUS  COLORS? 

A.  Because  all  these  colors  have 
different  refractive  susceptibilities.  Red 
is  refracted  least,  and  blue  the  most ; 
therefore,  the  blue  color  of  the  ray  will 
be  bent  to  the  top  of  the  prism,  and  the 
red  will  remain  at  the  bottom. 


B 

Here  the  ray  AB  (received  on  a  prism  at  B),  would 


RAINBOW. 


365 


have  the  blue  part  bent  up  to  C ;  the  yellow  part  to  D ; 
and  the  red  part  no  further  than  E. 

Q.  What  is  meant  by  the  REFRACTION  of  a 
ray  ? 

A.     Bending  it  from  its  straight  line. 

Thus  the  ray  AB  of  the  last  figure  is  refracted  at  B  into 
three  courses,  C,  D,  and  E. 

Q.       What  is  the  cause  of  a  RAINBOW  ? 

A.  When  the  clouds  opposite  the  sun 
are  very  dark,  and  rain  is  still  falling 
from  them,  the  rays  of  the  bright  sun 
are  divided  by  the  rain-drops^  as  they 
would  be  by  a  prism. 


Let  A,  B,  and  C,  be  three  drops  of  rain ;  SA,  SB,  and 
SO,  three  rays  of  the  sun.  SA  is  divided  into  three  col- 
ors ;  the  blue  and  yellow  are  bent  above  the  eye  D,  and  the 
red  enters  it. 

The  ray  SB  is  divided  into  the  three  colors ;  the  blue  is 
bent  above  the  eye,  and  the  red  falls  below  the  eye  D ;  but 
the  yellow  enters  it. 

The  ray  SC  is  also  divided  into  the  three  colors.  The 
blue  (which  is  bent  most)  enters  the  eye ;  and  the  other 


366  LIGHT. 

two  fall  below  it.  Thus  the  eye  sees  the  blue  of  C,  and 
of  all  drops  in  the  position  of  C ;  the  yellow  of  B,  and  of 
all  drops  in  the  position  of  B  ;  and  the  red  of  A,  and  of 
all  drops  in  the  position  of  A  ;  and  thus  it  sees  a  rainbow. 

Q.  Does  EVERY  person  see  the  SAME  colors  from 
the  SAME  DROPS  ? 

A.  No  ;  no  two  persons  see  the  same 
rainbow. 

To  another  spectator,  the  rays  from  SB  might  be  red 
instead  of  yellow ;  the  ray  from  SC  yellow ;  and  the  blue 
might  be  reflected  from  some  drop  below  C.  To  a  third 
person,  the  red  may  issue  from  a  drop  above  A,  and  then 
A  would  reflect  the  yellow,  and  B  the  blue,  and  so  on. 

Q.  Why  are  there  often  TWO  RAINBOWS  at  one 
and  the  same  time  ? 

A.  In  one  rainbow  we  see  the  rays 
of  the  sun  entering  the  rain-drops  at  the 
top,  and  reflected  to  the  eye  from  the 
bottom. 

In  the  other  rainbow,  we  see  the  rays 
of  the  sun  entering  the  rain-drops  at  the 
bottom,  and  reflected  to  the  top,  whence 
they  reach  the  eye. 


Here  the  ray  SA  (of  the  primary  rainbow)  strikes  the 
drop  at  A— is"  refracted  or  bent  to  B— is  then  reflected 


COLORS    OF    THE    RAINBOW.  367 

to  C,  where  it  is  refracted  again,  and  reaches  the  eye  of 
the  spectator.    (See  below.) 


Here  the  ray  of  SB  (of  the  secondary  rainbow)  strikes 
the  drop  at  B — is  refracted  to  A — is  then  reflected  to  C 
— is  again  reflected  to  D,  when  it  is  again  refracted  or 
bent,  till  it  reaches  the  eye  of  the  spectator. 

Q.       Why  are  the  COLORS  of  the  SECOND  bow  all 

REVERSED  ? 

A.  Because  in  one  bow  we  see  the 
rays,  which  enter  at  the  top  of  the  rain- 
drops, refracted  from  the  bottom : 

But  in  the  other  bow  we  see  the  rays 
which  enter  at  the  bottom  of  the  rain- 
drops (after  two  reflections),  refracted 
from  the  top. 

See  figure  on  next  page. 

Here  ABC  represent  three  drops  of  rain  in  the  SECON- 
DARY (or  upper)  RAINBOW. 

The  least  refracted  line  is  RED,  and  BLUE  the  most. 

So  the  RED  (or  least  refracted  rays)  of  all  the  drops  in 
the  position  of  A — the  YELLOW  of  those  in  the  position 
of  B — and  the  BLUE  (or  the  most  refracted  rays)  of  the 
lowest  drops,  all  meet  the  eye  D,  and  form  a  rainbow  to 
the  spectator. 

The  reason  why  the  primary  bow  exhibits  the  stronger 
colors  is  this — because  the  colors  are  seen  after  one  refleo 


368 


LIGHT. 


ijj  jif  S1 


lion  and  two  refractions ;  but  the  colors  of  the  secondary 
(or  upper)  rainbow,  undergo  tioo  reflections  and  two  re- 
fractions. 

(See  figure  on  p.  365.)  Here  also  the  least  refracted  ray 
is  RED,  and  the  most  refracted  BLUE  (as  in  the  former  case)  ; 
but  the  position  of  each  is  reversed. 

Q.  Why  does  a  SOAP  BUBBLE  exhibit  such  a 
VARIETY  of  COLORS? 

A.  Because  the  thickness  of  the  film 
through  which  the  rays  pass,  is  con- 
stantly varying*. 

Q.  How  does  the  THICKNESS  of  the  FILM  affect 
the  COLOR  of  the  soap  bubble  ? 

A.  Because  different  degrees  of  thick- 
ness in  the  film  produce  different  powers 
of  refraction ;  and,  therefore,  as  the  thick- 
ness of  the  film  varies,  different  colors 
reach  the  eye. 

Q.       Why  is  a  SOAP    BUBBLE   so    constantly 

CHANGING  its  THICKNESS  1 


RAYS. 


369 


A.  Because  the  water  runs  down 
from  the  top  to  the  bottom  of  the  bubble, 
till  the  crown  becomes  so  thin  as  to 
burst. 

Q.       Why  are  the  late  EVENING  CLOUDS  RED  ? 

A.  Because  RED  rays,  being-  the  least 
refrangible,  are  the  last  to  disappear. 


Suppose  PA  to  be  a  red  ray,  PB  yellow,  and  PC  blue — 
if  the  earth  turns  in  the  direction  of  CBD,  it  is  quite  man- 
ifest that  a  spectator  standing  at  C  or  B  (carried  round 
in  the  same  direction),  would  lose  sight  of  the  red  rays 
(A)  last  of  all. 

Q.       Why  are  the  early  MORNING  clouds  RED  ? 

A.  Because  RED  rays  being  the  least 
refrangible  are  theirs/  to  appear. 

See  last  figure. — We  must  suppose  the  sun  to  be  on  the 
left  side  of  the  diagram — or  (what  will  answer  the  same 
purpose)  suppose  the  earth  to  be  turning  in  the  direction 
of  BAP,  then  it  is  quite  clear,  that  every  person  on  the 
earth's  surface  will  pass  under  A  (the  red  rays)  before  he 
passes  under  B  or  C,  (and  therefore  his  early  morning 
rays  will  be  red.) 

Q.       Why  are  the  EDGES  of  CLOUDS  more  LUMIN- 
ws  than  their  CENTRES  ? 
16* 


370  LIGHT. 

A.  Because  the  body  of  vapor  \s  thin" 
nest  at  the  edges  of  the  clouds. 

Q.       What  is  the  cause  of  morning  and  evening 

TWILIGHT  ? 

A.  When  the  sun  is  below  the  hori- 
zon, the  rays  which  strike  upon  the 
atmosphere  or  clouds  are  bent  down 
towards  the  earth,  and  produce  a  little 
light  called  twilight. 

See  figure  on  p.  369. — Here  the  rays  of  PA  will  give  somt 
light. 

Q.  WHY  is  a  ray  of  LIGHT  composed  of  VARI- 
OUS COLORS  ? 

A.  To  vary  the  color  of  different 
objects.  If  solar  light  were  of  one  color 
only,  all  objects  would  appear  of  that  one 
color,  or  else  black. 

Q.  Some  things  are  of  ONE  COLOR,  and  some 
0f  ANOTHER..  JElxplain  tlie  cause  of  this. 

A.  As  every  ray  of  light  is  composed 
of  all  the  colors  of  the  rainbow ;  some 
things  reflect  one  of  these  colors  and  some 
another. 

Q.  WHY  do  some  things  reflect  ONE  COLOR,  and 
some  ANOTHER  ? 

A.  Because  the  surface  of  things  is 
so  differently  constructed,  both  physically 
and  chemically. 

Q.       Why  is  a  ROSE  RED  ? 

A.     Because  the  surface  of  a  rose  ab- 


COLOR.  371 

sorbs  the  blue  and  yellow  rays  of  light, 
and  reflects  only  the  red. 

Q.       Why  is  a  VIOLET  BLTJE  ? 

A.  Because  the  surface  of  the  violet 
absorbs  the  red  and  yellow  rays  of  the  sun, 
and  rejlects  the  blue  only. 

Q.       Why  is  a  PRIMROSE  YELLOW  1 
A.     Because  the  surface  of  the  prim- 
rose absorbs  the  blue  and  red  rays  of  solar 
light,  and  rejlects  the  yellow. 

The  chief  reason  why  some  rays  are  absorbed  and  other? 
reflected  is,  because  the  corpuscles  which  compose  the  col- 
ored substance  vary  in  magnitude : — thus,  for  example,  if 
the  diameter  of  a  corpuscle  of  equal  density  with  air  be 
21  millionth  of  an  inch,  it  will  reflect  purple;  if,  on  the 
other  hand,  it  be  29  millionth  of  an  inch,  it  will  reflect 
red,  and  so  on. 

Q.       Why  are  some  things  BLACK  ? 

A.  Because  they  absorb  all  the  rays 
of  light  and  reflect  none. 

Q.       Why  are  some  things  WHITE  ? 

A.  Because  they  absorb  none  of  the 
rays  of  light,  but  reflect  them  all. 

Q.       Why  are  COALS  BLACK  ? 

A.  Because  they  absorb  all  the  rays 
of  the  sun  which  impinge  upon  them. 

Q.       Why  are  FROTH,  and  SPRAY,  and  many 

CLOUDS,  WHITE  ? 

A.  Because  they  consist  of  an  infinite 
number  of  small  bubbles  or  vesicles, 
which  act  like  prisms  in  dividing  the 


372  LIGHT. 

rays  of  light;  which,  by  uniting  again 
before  they  meet  the  eye,  give  the  ap- 
pearance of  white. 

Q.       Why  are  SNOW,  SUGAR,  and  SALT  WHITE? 

A.     (See  page  312.) 

N.  B.  The  combination  of  all  colors  makes  WHITE. 
Q.       Why  are  the  LEAVES  of  plants  GREEN  ? 

A.  Because  a  peculiar  chemical  prin- 
ciple, called  chlo'rophyll,  is  formed  within 
their  cells ;  which  has  the  property  of 
absorbing  the  red  rays  and  of  reflecting 
the  blue  and  yellow ;  which  mixture 
produces  green. 

Chlorophyll  (^Awpoy  <j>v\\ov,  a  green  leaf)  is  the  green 
matter  of  vegetable  substances.     Pronounce  klo-ro-fill. 

Q.       Why  are  leaves  a  LIGHT  green  in  SPRING  ? 

A.  Because  the  chlo'rophyll  is  not 
fully  formed. 

Q.       Why  do  leaves  turn  BROWN  in  AUTUMN  ? 

A.  Because  the  chlo'rophyll  under- 
goes decay,  and  is  not  replaced  as  it  is 
in  spring. 

Q.  Why  are  plants  a  PALE  YELLOW,  when 
kept  in  the  DARK  ? 

A.  Because  chlo'rophyll  can  be  form- 
ed only  by  the  agency  of  the  surfs  rays. 

Q.       Why  are  POTATOES  YELLOW  ? 

A.  Because  they  are  grown  under- 
ground ;  and,  therefore,  can  form  no 
chlo'rophyll  in  their  tubers. 


TRANSPARENCY.  373 

Q.  Why  are  potatoes  which  grow  EXPOSED  to 
the  air  arid  light  GREEN  ? 

A.  Because  chlo'rophyll  is  formed  in 
them  under  the  influence  of  the  sun's 
light. 

Q.       Why  are  SOME  things  TRANSPARENT  ? 

A.  Because  every  part  between  the 
two  surfaces  has  a  uniform  refracting 
power,  or  (in  other  words)  has  in  every 
place  the  same  density. 

And,  therefore,  the  rays  of  light  emerge  on  the  opposite 
side. 

Q.       Why  are  some  things  NOT  TRANSPARENT? 

A.  Because  the  particles  which  com- 
pose them  are  separated  by  minute  pores 
or  spaces,  which  have  a  different  density 
from  the  particles  themselves. 

Therefore,  the  rays  of  light  are  reflected  and  refracted 
too  often  to  emerge. 

Q.  Why  are  DRY  PAPER  and  calico  (which  are 
OPAQUE)  made  transparent  by  being  OILED? 

A.  Because  the  pores  are  filled  by 
the  oil,  which  has  nearly  the  same  den- 
sity as  the  substance  of  the  paper  itself 
— by  which  means  a  uniform  density  is 
effected,  and  the  substance  becomes 
transparent. 

Q.  Why  is  GLASS  (which  is  transparent)  ren- 
dered OPAQUE  by  being  ground  or  pulverized  ? 

A.     Because    the    whole    substance 


374  LIGHT. 

from  surface  to  surface  is  no  longer  of 
one  uniform  density. 

Q.  Why  are  SOME  things  SHINING,  and  others 
DULL? 

A.  Because  some  thing's  reflect  rays, 
and  are  bright ;  but  others  absorb  them. 

Q.       Why  do  DESERTS  DAZT.UE.  from  sunshine? 

A.  Because  each  grain  of  sand  reflects 
the  rays  of  the  sun  like  a  mirror. 

Q.  If  you  move  a  stick  (burnt  at  one  end) 
pretty  briskly  AROUND,  it  seems  to  make  a  CIRCLE 
OF  FIRE — WHY  is  this  ? 

A.  Because  the  eye  retains  the  image 
of  any  bright  object,  after  the  object  itself 
is  withdrawn ;  and  as  the  spark  of  the 
stick  returns  before  the  image  has  faded 
from  the  eye,  it  seems  to  form  a  complete 
circle. 

Q.  If  separate  figures  (as  a  man  and  a  horse) 
be  drawn  on  separate  sides  of  a  card,  and  the  card 
TWISTED  quickly^  the  man  will  seem  to  be  seated  on 
the  horse — WHY  is  this? 

A.  Because  the  image  of  the  horse 
remains  upon  the  eye  till  the  man  ap- 
pears. 

The  Thaumatrope  is  constructed  on  this  principle. 
Q.       Why  do  the  STARS  TWINKLE  ? 

A.  Because  the  inequalities  and  un- 
dulations in  the  atmosphere  produce  un- 
equal refractions  of  light;  and  these 


ACCIDENTAL    COLORS.  375 

unequal  refractions  cause  the  twinkling 
or  irregular  brilliancy  of  the  stars. 

Q.  If  we  look  at  a  RED-HOT  FIRE  for  a  few 
minutes,  WHY  does  every  thing  seem  TINGED  with  a 

BLUISH  GREEN  Color  ? 

A.  Because  bluish  green  is  the 
"  ACCIDENTAL  COLOR  "  of  red  ;  and  if  we 
fix  our  eye  upon  any  color  whatsoever, 
we  see  every  object  tinged  with  its  acci- 
dental color  when  we  turn  aside. 

The  accidental  color  is  the  color  which  would  be  required 
to  be  added,  in  order  to  make  up  white  light.     See  p.  360. 

Q.  Why  does  the  eye  perceive  the  ACCIDENTAL 
COLOR  when  the  fundamental  one  is  removed? 

A.  Because  the  nerve  of  the  eye  has 
become  tired  of  the  one,  but  still  remains 
fresh  for  the  perception  of  the  other. 

Q.  If  we  wear  BLUE  GLASSES,  why  does  every 
thing  appear  tinged  with  ORANGE  when  we  take  them 
of? 

A.  Because  orange  is  the  "  accidental 
color  "  of  blue  ;  and  if  we  look  through 
blue  glasses,  we  shall  see  its  "  accidental 
color  "  when  we  lay  our  glasses  aside. 

Q.  If  we  look  at  the  SUN  for  a  few  moments, 
every  thing  seems  tinged  with  a  VIOLET  color — Wnt 
is  Ms  ? 

A.  Because  violet  is  the  "  accidental 
color  "  of  yellow ;  ,and  as  the  sun  is  yd- 
low,  we  shall  see  its  "  accidental  color  " 
violet  when  we  turn  from  gazing  at  it. 


376  LIGHT. 

Q.  Does  not  the  DARK  SHADOW  (which  seems  to 
hang  over  every  thing  after  we  turn  from  looking  at 
the  su?i)  arise  from  our  eyes  being  DAZZLED  ? 

A.  Partly  so  :  the  pupil  of  the  eye  is 
very  much  contracted  by  the  brilliant  light 
of  the  sun,  and  does  not  adjust  itself  im- 
mediately to  the  feebler  light  of  terres- 
trial objects ;  but,  independent  of  this, 
the  "  ACCIDENTAL  COLOR  "  of  the  sun  be- 
ing dark  violet,  would  tend  to  throw  a 
shadow  upon  all  things.  (See  p.  340.) 

Q.  Why  is  BLACK  glass  for  spectacles  the  BEST 
for  wear  in  this  respect  ? 

A.  Because  white  is  the  accidental 
color  of  black ;  and  if  we  wear  black 
glasses,  every  thing  will  appear  in  ivhite 
light  when  we  take  them  off. 

Q.  Why  does  every  thing  seem  shadowed  with 
a  BLACK  MIST  when  we  take  off  our  common  SPECTA- 
CLES ? 

A.  Because  the  glasses  are  white ; 
and  black  being  its  "  accidental  color/7 
every  thing  appears  in  a  black  shade  when 
we  lay  our  glasses  down. 

The  accidental  color  of  red        is  bluish  green. 
"     of  orange  "  blue. 
"     of  violet     "  yellow. 
"     of  black     "  white. 
And  the  converse  of  this  is  true  : — 

The  accidental  color  of  bluish  green  is  red. 

"     of  blue    '          "  orange. 
"     of  yellow          "  violet. 
"  "  "     of  white  "black. 


SOUND.  377 

(The  law  of  an  accidental  color  is  this — The  accidental 
color  is  always  half  the  spectrum.  Thus,  if  we  take  half 
the  length  of  the  spectrum  by  a  pair  of  compasses,  and 
fix  one  leg  in  any  color,  the  other  leg  will  hit  upon  its  ac- 
cidental color.) 

N.  B.  The  spectrum  means  the  seven  colors  (red,  or- 
ange, yellow,  green,  blue,  indigo,  and  violet),  divided  into 
seven  equal  bands,  and  placed  side  by  side  in  the  order  just 
mentioned. 


SOUND. 

CHAPTER  XXX. 

Q.      How  is  SOUND  produced  ? 

A.  The  vibration  of  some  sonorous 
substance  produces  motion  in  the  air, 
called  SOUND-WAVES,  which  strike  upon 
the  drum  of  tlie  ear  and  give  the  sensa- 
tion of  sound. 

Q.       What  are  MUSICAL  SOUNDS  ? 

A.  Regular  and  uniform  successions 
of  vibrations. 

Q.       How  FAST  does  SOUND  TRAVEL  ? 

A.  About  13  miles  in  a  minute,  or 
1142  feet  in  a  second  of  time. 

Light  would  go  480  times  round  the  whole  earth,  while 
sound  is  going  its  13  miles. 

Q.  Why  are  SOME  things  SONOE.OUS  and  others 
NOT? 

A.  The  sonorous  quality  of  any  sub- 
stance depends  upon  its  hardness  and 
elasticity. 


378  SOUND. 

Q.  Why  are  COPPER  ana  IRON  SONOROUS  and. 
not  LEAD  ? 

A.  Copper  and  iron  are  hard  and 
clastic;  but  as  lead  is  neither  hard  nor 
yet  elastic,  it  is  not  sonorous. 

Q.       Of  what  is  BELL-METAL  made  ? 

A.  Of  copper  and  tin  in  the  following* 
proportions  : — In  every  5  pounds  of  bell- 
metal  there  should  be  1  pound  of  tin, 
and  4  pounds  of  copper. 

Q.       Why  is  this  mixture  of  tin  and  copper  used 

for  BELL-METAL? 

A.  Because  it  is  much  harder  and 
more  elastic  than  any  of  the  pure  metals. 

Q.  Why  is  the  SOUND  of  a  bell  STOPPED  by 
TOUCHING  the  bell  with  our  finger  ? 

A.  Because  the  weight  of  our  finger 
stops  t/ie  vibrations  of  the  bell ;  and  as 
soon  as  the  bell  ceases  to  vibrat,e,  it  ceases 
to  make  sound-waves  in  the  air. 

Q.  Why  does  a  SPLIT  BELL  make  a  hoarse,  dis- 
agreeable sound  ? 

A.  Because  the  split  of  the  bell 
causes  a  double  vibration :  And  as  the 
sound-waves  clash  and  jar,  they  impede 
each  other's  motion,  and  produce  dis- 
cordant sounds. 

Q.  Why  does  a  FIDDLE-STRING  give  a  musical 
sound  ? 

A.  Because  the  bow  drawn  across 
the  string  causes  it  to  vibrate ;  and  this 


MUSICAL    SOUNDS.  379 

vibration  of  the  string  sets  in  motion  the 
sound-waves  of  the  air,  arid  produces 
musical  notes. 

Q.       Why  does  a  DRUM  sound  ? 

A.  Because  the  parchment  head  of 
the  drum  vibrates  from  the  blow  of  the 
drum-stick,  and  sets  in  motion  the  sound- 
waves of  the  air. 

Q.       Why  do  MUSICAL  GLASSES  give  sounds  1 

A.  Because  the  glasses  vibrate  as 
soon  as  they  are  struck,  and  set  in  motion 
the  sound-waves  of  the  air. 

Q.  Why  do  FLUTES,  <^c.,  produce  musical 
sounds  ? 

A.  Because  the  breath  of  the  per- 
former causes  the  air  in  the  flute  to  vi- 
brate ;  and  this  vibration  sets  in  motion 
the  sound-waves  of  the  air. 

Q.  Why  do  PIANO-FORTES  produce  musical 
sounds  ? 

A.  Because  each  key  of  the  piano 
(being  struck  with  the  finger)  lifts  up  a 
little  hammer  which  knocks  against  a 
string  ;  and  the  vibration  thus  produced 
sets  in  motion  the  sound-waves  of  the  air. 

Q.  Why  are  SOME  notes  BASS,  and  SCWl€  TRE- 
BLE ? 

A.  Because  slow  vibrations  produce 
bass  or  deep  sounds  ;  but  quick  vibrations 
produce  shrill  or  treble  ones. 


380  SOUND. 

Q.  Why  is  an  instrument  FLAT  when  tht 
STRINGS  are  UNSTRUNG  ? 

A.  Because  the  vibrations  are  too 
slow ;  in  consequence  of  which,  the 
sounds  produced  are  not  shrill  or  stiarp 
enough. 

Q.  Why  can  per  sons,  living  a  mile  or  two  from 
a  town,  HEAR  the  BELLS  of  the  town  churches  SOME- 
TIMES and  not  at  OTHERS  ? 

A.  Because  fogs,  rain,  and  snow, 
obstruct  the  passage  of  sound  ;  but  when 
the  air  is  cold  and  clear,  sound  is  propa- 
gated more  easily. 

Q.  WHY  can  we  NOT  hear  sounds  (as  those  of 
distant  church  bells)  in  RAINY  weather  so  well  as  in 
FINE  weather? 

A.  Because  the  falling  rain  interferes 
with  the  undulations  of  the  sound-waves, 
and  breaks  them  up. 

Q.  Why  can  we  not  hear  sounds  (as  those  of 
distant  church  bells)  in  SNOWY  weather  so  well  as  in 
FINE  weather  ? 

A.  Because  the  falling  snow  inter- 
feres with  the  undulations  of  the  sound- 
leaves,  and  stops  their  progress. 

Q.  Why  can  we  HEAR  distant  clocks  MOST  dis- 
tinctly in  CLEAR  COLD  iveather  ? 

A.  Because  the  air  is  of  more  uniform 
density,  and  there  are  fewer  currents  of 
air  of  unequal  temperature  to  interrupt 
the  sound-waves. 


DISTANT    SOUNDS.  381 

Besides,,  dense  air  can  propagate  sound-waves  more 
readily  than  rarer  air. 

Q.  Why  can  persons  (near  the  POLES)  hear  the, 
VOICES  of  men  in  conversation  for  a  MILE  distant  in 
winter-time  ? 

A.  Because  the  air  is  very  cold,  clear, 
and  still;  in  consequence  of  which,  there 
are  but  few  currents  of  air  of  unequal 
temperature  to  interrupt  the  sound- 
waves. 

Captain  Ross  heard  the  voices  of  his  men  in  conversa- 
tion a  mile  and  a  half  from  the  spot  where  they  stood. 

Q.  Why  are  not  SOUNDS  (such  as  those  of  dis- 
tant church  bells)  heard  so  distinctly  on  a  HOT  DAY 
as  in  FROSTY  weather  ? 

A.  1st — Because  the  density  of  the 
air  is  less  uniform  in  very  hot  weather : 

2dly — It  is  more  rarefied  ;  and,  conse- 
quently, a  worse  conductor  of  sound :  and 

3dly — It  is  more  liable  to  accidental 
currents,  which  impede  the  progress  of 
sound. 

Q.  Why  can  we  not  hear  SOUNDS  (such  as 
those  of  distant  clocks)  so  distinctly  in  a  thick  MIST 
or  HAZE  as  in  a  CLEAR  night  ? 

A.  Because  the  air  is  not  of  uniform 
density  when  it  is  laden  with  mist ;  in 
consequence  of  which,  the  sound-waves 
are  obstructed  in  their  progress. 

Q.  Why  do  we  hear  SOUNDS  better  by  NIGHT 
than  by  DAY  ? 

A.     1st — Because  night  air  is  of  more 


382  SOUND. 

uniform  density  and  less  liable  to  acd~ 
denial  currents :  and 

2dly — Night  is  more  still  from  the 
suspension  of  business  and  hum  of  men. 

Q.  Why  is  the  air  of  more  UNIFORM  DENSITY 
by  NIGHT  than  it  is  by  day  ? 

A.  Because  it  is  less  liable  to  acci- 
dental currents  ;  inasmuch  as  the  breez- 
es (created  by  the  action  of  the  sun's 
rays)  generally  cease  during-  the  night. 

Q.  How  should  PARTITION  WALLS  be  made,  to 
PREVENT  the  voices  in  adjoining  rooms  from  being 

HEARD  ? 

A.  The  space  between  the  laths 
should  be  filled  with  shavings  or  saw- 
dust; and  then  no  sound  would  ever 
pass  from  one  room  to  another. 

Q.  Why  would  SHAVINGS,  or  saw-dust,  PRE- 
VENT the  transmission  of  sound  from  room  to  room  ? 

A.  Because  there  would  be  several 
different  media  for  the  sound  to  pass 
through:  1st — the  air;  2dly — the  laths 
and  paper ;  3dly — the  saw-dust  or  sha- 
vings ;  4thly — lath  and  paper  again  ; 
5thly— the  air  again  :  And  every  change 
of  medium  diminishes  the  strength  of  the 
sound-waves. 

Q.       Why  can  DEAF  people  hear  through  an 

EAR-TRUMPET? 

A.     Because  the  ear-trumpet  restrains 


ECHO.  383 

the  spread  of  the  voice  and  limits  the  dia- 
meter of  the  sound-waves :  in  consequence 
of  which,  their  strength  is  increased. 

Q.       Why  are  MOUNTAINS  NOISELESS  andyuiet  ? 

A.  Because  the  air  of  mountains  is 
very  rarejied;  and,  as  the  air  becomes 
rarefied,  sound  becomes  less  intense. 

Q.  How  do  you  know  that  the  RARITY  of  air 
DIMINISHES  the  intensity  of  SOUND  ? 

A.  If  a  bell  be  rung  in  the  receiver 
of  an  air-pump,  the  sound  becomes 
fainter  and  fainter  as  the  air  is  exhaust- 
ed ;  till  at  last  it  is  almost  inaudible. 

Q.       What  is  the  cause  of  ECHO  ? 

A.  Whenever  a  sound-wave  strikes 
against  any  obstacle  (such  as  a  wall  or 
hill),  it  is  reflected  (or  thrown  back)  ;  and 
this  reflected  sound  is  called  an  ECHO. 

The  same  laws  govern  echo  as  light.     (See  p.  338.) 
Q.       What  places  are  most  famous  for  ECHO  ? 

A.  Caverns,  grottoes,  and  ruined  ab- 
beys ;  the  areas  of  halls ;  the  windings 
of  long  passages  ;  the  aisles  of  cathedral 
churches  ;  mountains  and  icebergs. 

Q.       Why  are  caverns,  grottoes,  and  ruins ,  FA- 

MOUSjfor  ECHOES  ? 

A.  1st — Because  the  sound-waves 
cannot  pass  beyond  the  cavern  or  grotto, 
and,  therefore,  must  flow  back :  and 

2dly — The  return-waves  (being  entan- 


384  SOUND. 

gled  by  the  cavern)  are  detained  for  a 
short  time,  and  come  deliberately  to  the 
ear. 

Q.  Why  are  halls,  winding  passages^  and  ca- 
thedral aisles,  FAMOUS  for  ECHOES? 

A.  Because  the  sound-waves  cannot 
flow  freely  forward;  but  perpetually 
strike  against  the  winding  walls,  and 
are  beaten  back. 

Q.  Why  are  MOUNTAINS  and  icebergs  FAMOUS 
for  ECHOES  ? 

A.  Because  they  present  a  barrier  to 
the  sound-waves,  which  they  cannot  pass, 
and  are  sufficiently  elastic  to  throw  them 
back. 

Q.  Why  do  not  the  WALLS  of  a  ROOM  or  church 
produce  ECHO  ? 

A.  Because  sound  travels  with  such 
velocity  that  the  echo  is  blended  with  the 
original  sound;  and  the  two  produce 
but  one  impression  on  the  ear. 

Sound  travels  13  miles  in  a  minute;  and  no  echo  is 
heard,  unless  the  surface  (against  which  the  sound  strikes) 
is  65  feet  from  the  place  whence  the  sound  originally  pro- 
ceeded. x 

Q.  Why  do  very  LARGE  buildings  (as  cathe- 
drals) often  REVERBERATE  the  voice  of  the  speaker  ? 

A.  Because  the  walls  are  so  far  off 
from  the  speaker  that  the  echo  does  not 
get  back  in  time  to  blend  with  the  origi- 


ECHO.  385 

nal  sound  ;  and,  therefore,  each  is  heard 
separately. 

Q.  Why  do  SOME  echoes  repeat  only  ONE  sylla- 
ble? 

A.  Because  the  echoing*  body  is  very 
near.  The  further  the  echoing-  body  is 
off,  the  more  sound  it  will  reflect:  If, 
therefore,  it  be  very  near,  it  will  repeat 
but  one  syllable. 

Q.  Why  does  an  ECHO  sometimes  repeat  TWO 
or  more  syllables  ? 

A.  Because  the  echoing*  body  is  far 
off ;  and,  therefore,  there  is  time  for  one 
reflection  to  pass  away  before  another 
reaches  the  ear. 

N.  B.  All  the  syllables  must  be  uttered,  before  the  echo 
of  the  first  syllable  reaches  the  ear — If,  therefore,  a  per- 
son repeats  7  syllables  in  2  seconds  of  time,  and  hears 
them  all  echoed,  the  reflecting  object  is  1142 feet  distant; 
(because  sound  travels  1142  feet  in  a  second,  and  the 
words  take  one  second  to  go  to  the  reflecting-  object,  and 
one  second  to  return.) 

Q.  Why  are  TWO  or  more  ECHOES  sometimes 
heard  ? 

A.  Because  separate  reverberating* 
surfaces  receive  the  sound  and  reflect 
it  in  succession. 

17  miles  above  Glasgow  (Scotland)  near  a  mansion  called 
Rosneath,  is  a  very  remarkable  echo.  If  a  trumpeter 
plays  a  tune  and  stops,  the  echo  will  begin  the  same  tune 
and  repeat  it  all  accurately : — as  soon  as  this  echo  has 
ceased,  another  will  echo  the  same  tune  in  a  lower  tone; 
and  after  the  second  echo  has  ceased,  a  third  will  succeed 
with  equal  fidelity,  though  in  a  much  feebler  tone. 
17 


386  WINDOWS. 

At  the  Lake  of  Kilkarney  in  IRELAND,  there  is  an  echo 
which  plays  an  excellent  "  second "  to  any  simple  tune 
played  on  a  bugle. 

Q.  Why  do  WINDOWS  RATTLE  when  CARTS 
pass  by  a  house  ? 

A.  1st — Because  glass  is  sonorous ; 
and  the  air  communicates  its  vibrations 
to  the  glass,  which  echoes  the  same 
sound  :  and 

2dly  The  window-frame  being  sha- 
ken, contributes  to  the  noise. 

Window  frames  are  shaken,  1. — By  sound-waves  im- 
pinging against  them ;  2. — By  a  vibratory  motion  com- 
municated to  them  by  the  walls  of  the  house. 


PART    III. 
MISCELLANEOUS. 


***  This  part  is  little  else  than  a  collection  of  various 
questions  propounded  by  different  correspondents,  pupils, 
and  private  friends,  set  down,  without  regard  to  arrange- 
ment, in  the  order  in  which  they  were  proposed  ;  together 
with  a  few  leading  questions  to  break  up  some  which 
would  have  been  otherwise  too  intricate,  and  others  which 
naturally  arose  out  of  the  subject  under  consideration. 

Q.  Why  do  the  BUBBLES  in  a  CUP  of  TEA  range 
round  the  SIDES  of  the  CUP  ? 

A.     Because  the  cup  attracts  them. 

Q.  Why  do  all  the  LITTLE  BUBBLES  tend  to- 
wards the  LARGE  ones  ? 

A.  Because  the  large  bubbles  (being1 
the  superior  masses)  attract  them. 

Q.       Why   do  the  BUBBLES  of  a   CUP   OF  TEA 

FOLLOW  a  TEA-SPOON  ? 

A.  Because  the  tea-spoon  attracts 
them. 

Q.  Why  are  the  SIDES  of  a  pond  covered  with 
LEAVES,  while  the  MIDDLE  of  the  pond  is  quite 

CLEAR  ? 


388  CAPILLARY    ATTRACTION. 

A.  Because  the  shore  attracts  the 
leaves  to  itself.  * 

Q.  Why  do  all  fruits,  fyc.,  (when  severed  from 
the  tree.)  FALL  to  the  EARTH  ? 

A.     Because  the  earth  attracts  them. 

Q.  Why  do  persons  who  water  PLANTS  very 
often  'pour  the  ivatcr  into  the  SAUCER,  and  not  aver 
the  PLANTS  ? 

A.  Because  the  water  in  the  saucer 
is  drawn  up  by  the  mould  (through  the 
hole  at  the  bottom  of  the  flower-pot) 
and  is  transferred  to  the  stem  and  leaves 
of  the  plant  by  CAPILLARY  ATTRACTION. 
(Seep.  75.) 

Q.  Why  is  vegetation  on  the  MARGIN  of  a  RIV- 
ER more  LUXURIANT  than  in  an  open  FIELD  ? 

A.  Because  the  porous  earth  on  the 
bank  draws  up  water  to  the  roots  of  the 
plants  by  CAPILLARY  ATTRACTION. 

Q.  Why  is  a  LUMP  of  SUGAR  (left  at  the  bottom 
of  a  cup)  so  LONG  in  MELTING? 

A.  Because  (as  it  melts)  it  makes  the 
tea  above  it  heavier ;  and  (so  long-  as  it 
remains  at  the  bottom)  is  surrounded  by 
tea  fully  saturated  with  sugar ;  in  con- 
sequence of  which,  the  same  portions  of 
liquid  will  hold  no  more  sugar  in  solution. 

Q.  Why  does  the  LUMP  of  SUGAR  MELT  more 
QUICKLY  when  STIRRED  ABOUT  1 

A.     Because  fresli  portions  of  unsatw- 


EFFLUVIA. 


389 


rated  tea  come  in  contact  with  the  lump, 
and  soon  dissolve  it. 

Q.  Why  does  a  PIECE  OP  SUGAR  (held  in  a 
spoon  at  the  TOP  of  our  tea)  melt  very  RAPIDLY? 

A.  Because,  as  the  tea  becomes 
sweetened,  it  descends  to  the  bottom  of  the 
cup  by  its  own  gravity ;  and  fresh  por- 
tions of  unsweetened  tea  are  brought 
constantly  into  contact  with  the  sugar 
till  the  lump  is  entirely  dissolved. 

Q.  How  can  a  SICK  ROOM  be  kept  FREE  from 
unhealthy  EFFLUVIA? 

A.  By  sprinkling  it  with  vinegar 
boiled  with  myrrh  or  camphor. 

Q.       Why  does  LIME  destroy  the  offensive  smells 

Of  BINS,  SEWERS,  <SfC.  ? 

A.  Because  it  decomposes  the  offen- 
sive gases  upon  which  the  smell  depends, 
and  destroys  them. 

Q.  Why  does  CHLORIDE  of  LIME  fumigate  a 
sick  room  ? 

A.  Because  the  chlorine  absorbs  the 
hydrogen  of  the  stale  air ;  and  by  this 
means  removes  both  the  offensive  smell 
and  the  infection  of  a  sick  room. 

Q.      How  can  the  TAINT  of  MEAT  be  removed  ? 

A.  Either  by  .washing  with  PYROLIG- 
NEOUS  ACID — or  by  covering  it  for  a  few 
hours  with  common  CHARCOAL — or  by 


390  TAINT    REMOVED. 

putting*  a  few  lumps  of  cJiarcoal  into  the 
water  in  which  it  is  boiled. 

Q.  Why  do  these  things  DESTROY  the  TAINT  of 
meat  ? 

A.  Because  they  combine  with  the 
putrescent  particles,  and  neutralize  their 
offensive  taste  and  smell. 

Q.  Why  should  BED-ROOMS,  COTTAGES,  HOS- 
PITALS, and  STABLES,  be  washed  occasionally  with 

LIME    WHITE? 

A.  Because  the  lime  is  very  caustic, 
and  removes  all,  organic  matters  adher- 
ing" to  the  walls. 

Q.  Why  will  strong  SOUCHONG  TEA  POISON 
FLIES  ? 

A.  Because  it  contains  prmsic  acidj 
which  destroys  their  nervous  system. 

Q.       Why  is  strong  GREEN  TEA  UNWHOLESOME  ? 

A.  Because  it  contains  prussic  acid, 
which  destroys  the  nervous  system. 

Q.  Why  is  a  DEAD  man  TALLER  than  a  living 
one? 

A.  Because  at  death  the  CARTILAGES 
are  relaxed.  So,  also,  after  a  night's 
rest,  a  man  is  taller  than  when  he  went 
to  bed. 

Q.       What  is  SLEEP  ? 

A.  Sleep  is  the  rest  of  the  brain  and 
nervous  system. 

Q.  Why  can  we  not  SEE,  when  we  are  asleep 
with  our  EYES  OPEN  ? 


THE    SENSES.  391 

A.  Because  the  "  RET'INA  of  the  eye" 
is  inactive  and  at  rest. 

Q.       Why  can  we  not  HEAR  in  sleep  ? 

A.  Because  the  nerve  of  hearing 
(seated  within  the  TYMPANUM  of  the  ear) 
is  at  rest. 

Q.       Why  can  we  not  TASTE  when  we  are  asleep  ? 

A.  Because  the  nerves  at  the  end  of 
the  tongue  (called  papillae)  are  inactive 
and  at  rest. 

Q.       Why  can  we  not  FEEL  when  we  are  asleep  ? 

A.  Because  the  ends  of  the  nerves 
(called  papillae)  situated  in  the  skin,  are 
inactive  and  at  rest. 

Q.  Why  have  per  sons  in  deep  no  WILL  of  their 
own,  but  may  be  moved  at  the  will  of  ANY  one  ? 

A.  Because  the  "CEREBELLUM"  (or 
posterior  part  of  the  brain)  is  inactive 
and  at  rest. 

Q.  Why  have  DREAMERS  no  power  of  JUDG- 
MENT or  REASON  ? 

A.  Because  the  "  CEREBRUM  "  (or 
front  of  the  brain)  is  inactive  and  at  rest. 

Q.       Why  do  some  persons  LOSE  all  POWER  of 

SENSATION  ? 

A.  Because  the  "  CEREBRUM  "  (or 
front  of  their  brain)  has  been  injured. 

Q.  Why  does  a  person  FEEL  when  he  is 
TOUCHED  ? 

A.     Because    the    ends    of    certain 


392  REFRACTION. 

nerves  (called  "  PAPILLAE")  situated  in  the 
skin,  are  excited;  and  produce  a  nervous 
sensation  called  FEELING. 

Q.  Why  a/re  persons  able  to  TASTE  DIFFERENT 
FLAVORS  1 

A.  Because  the  "  PAPILLA"  of  the 
tongue  and  palate  are  excited  when  food 
touches  them,  and  produce  a  nervous 
sensation  called  TASTE. 

Q.       Why  are  OLD  people  UNABLE  to  WALK  ? 

A.  Because  their  muscles  become 
rigid. 

Q.  Why  does  ABUNDANCE  of  DEW  in  the  morn- 
ing indicate,  that  the  day  will  be  FINE?  p.  189. 

A.  Because  dew  is  never  deposited 
in  dully  cloudy  weather,  but  only  in  very 
clear,  calm  nights ;  when  the  cold  currents 
of  air  are  not  mixed  with  those  of  a 
warmer  temperature.' 

Q.  Why  does  an  OAR  in  water  appear  bent  ? 
p.  358. 

A.  Because  the  part  out  of  the  water 
is  seen  in  a  different  medium  to  the  part 
in  the  water ;  and  the  rays  of  these  two 
parts,  meeting  together  at  the  surface  of 
the  river,  form  an  angle — or,  in  other 
words,  make  the  oar  look  as  if  it  were 
bent. 

As  all  the  rays  of  light  are  refracted  (or  bent)  more  in 
their  passage  through  water  than  in  their  passage  through 


COLOR.  393 

air,  they  will  tend  to  cross  each  other  at  the  surface  of 
the  water,  and,  of  course,  form  an  elbow  or  angle. 

Q.  If  a  piece  of  BROWN  PAPER  be  submitted  to 
the  action  of  a  BURNING  GLASS,  it  will  catch  fire 
much  SOONER  than  a  piece  of  white  paper  would ; 
Explain  the  reason,  p.  175. 

A.  Because  white  paper  reflects  the 
rays  of  the  sun,  or  throws  them  back ; 
in  consequence  of  which,  it  appears  more 
luminous,  but  is  not  so  much  heated,  as 
dark  brown  paper,  which  absorbs  the  rays 
and  readily  becomes  heated  to  ignition. 

Besides,  brown  paper  is  of  a  looser  and  more  combusti- 
ble fabric  than  white  paper. 

Q.       Why  does  a  lady's  BLUE  DRESS   appear 

GREEN  by  CANDLE  LIGHT  ?     pp.  76,  364. 

A.  Because  the  light  of  a  candle  is 
tinged  with  yellow ;  ajid  this  yellow  tinge, 
mixing  with  the  blue  dye  of  the  dress, 
produces  green. 

Q.  Why  does  the  SUN  look  red  in  a  FOG  ?  p. 
127. 

A.  Because  red  rays  have  a  greater 
momentum  than  any  other  rays ;  and 
this  superior  momentum  enables  them  to 
penetrate  the  dense  atmosphere  more 
readily  than  either  blue  or  yellow  rays, 
which  are  either  absorbed  or  reflected  by 
the  fog. 

"  Momentum  "  means,  the  impetus  or  power  ofpemtrai- 
ing  the  fog. 

17* 


394  INIQ-SPOTS. 

Q.       Why  is  an  INK-SPOT  on  linen  BLACK  when 
first  made? 

A.  Because  the  ink  produces  a  chemi- 
cal change  in  the  internal  condition  of 
the  fibres  of  the  linen,  by  which  it  loses 
its  power  of  reflecting  light ;  and,  as  it 
absorbs  the  rays  of  the  sun,  the  spot 
seems  black. 

The  black  color  of  ink  is  composed  of  a  compound  of 
Tannic  acid,  sesqui-oxide  of  iron,  and  water. 

"  Tannic  acid  "  is  an  acid  which  exists  in  oak  trees,  es- 
pecially in  the  bark,  but  is  abundant  in  nutgalls.  It  de- 
rives its  name  from  its  property  of  combining  with  the 
skins  of  animals  and  converting  them  into  leather,  which 
is  called  tanning  them. 

"  Sesqui-oxide  of  iron  "  means,  that  one  atom  and  a  half 
of  oxygen  is  mixed  with  one  atom  of  iron. — The  amount 
of  oxygen  in  an  oxide  is  always  expressed  by  some  similar 
affix,  thus 

Protoxide — 1  atom  of  oxygen  ^l 
Binoxide-2  atom,  of  oxV^n  I 
Teroxide-S^atoms  of  oxygen  | 

Per-oxide — the  highest  possible  degree  of  oxidation, 

&c. 
Sesqui-oxide— H  atom  of  oxygen  and  1  of  base. 

Q.  Why  does  the  black  ink-spot  on  linen  turn 
YELLOW  after  a  few  days  ? 

A.  Because  the  compound,  which 
composes  the  blackness  of  ink,  is  de- 
stroyed by  exposure  to  air  ;  and  the  linen 
partially  recovers  its  power  of  reflecting" 
colors,  but  with  a  preference  to  yellow 
rays. 

The  tannic  acid  and  water  are  in  a  measure  taken  up 
by  the  air,  and  the  oxide  of  iron  leaves  a  yellow  iron 
mould  behind. 


CANDLE    FLICKERING.  395 

Q.  Why  does  BRUSHING  the  HAIR  much  make 
the  head  itch?  p.  142. 

A.  1st— Because  the  friction  of  the 
hair-brush  excites  electricity  in  the  hair, 
which  thus  becomes  overcharged  and  ir- 
ritates the  skin :  and 

2dly — The  hair-brush  excites  in- 
creased action  in  the  vessels  and  nerves 
of  the  scalp,  producing  a  slight  degree  of 
inflammation,  which  is  indicated  by  a 
sensation  of  itching. 

Q.  Why  does  a  CANDLE  FLICKER,  especially 
just  previous  to  its  being  BURNT  OUT?  pp.  76,  80. 

A.  Because  it  is  unequally  supplied 
with  combustible  gases. — When  a  candle 
is  nearly  burnt  out,  there  is  not  sufficient 
tallow  or  wax  to  keep  up  the  regular 
supply  of  combustible  gas;  in  conse- 
quence of  which,  the  flame  flickers,  i.  e. 
blazes,  when  it  is  supplied  with  gas,  and 
goes  out  for  a  moment,  when  the  supply 
is  defective. 

Q.  If  the  "  COPPER"  (or  boiler)  attached  to  a 
kitchen  range,  be  filled  with  cold  water  AFTER  the  fire 
has  been  some  time  lighted,  it  will  very  often  CRACK 
(or  burst).  Why  is  this?  p.  118. 

A.  Because  the  heat  of  the  fire  has 
caused  the  "copper"  to  expand;  but 
the  cold  water  very  suddenly  condenses 
again  those  parts  with  which  it  comes  in 


396  FLAG-STONES. 

contact :  and,  as  one  part  is  larger  than 
the  other,  the  copper  cracks  or  bursts. 

Q.       What  is  color  ? 

A.  An  inherent  property  in  light. — 
The  reason  why  different  thing's  appear 
of  different  colors,  is  owing*  to  their  pow- 
er of  reflecting  some  rays  and  absorbing 
others. 

N.  B.  It  must  not  be  forgotten,  that  color  is  not  an  in- 
herent property  of  the  flower,  carpet,  rainbow,  &c.,  but  an 
inherent  property  of  the  light,  which  falls  upon  them. 

The  reason  why  one  thing  reflects  one  ray.  and  another 
thing  reflects  another  ray,  is  owing  to  the  different  thick- 
ness of  the  corpuscules  which  compose  them — the  acid  or 
alkaline  properties  of  their  juices  or  dyes — the  uniformity 
and  texture  of  their  parts — and  so  on ;  in  consequence  of 
which,  some  ray  or  rays  are  reflected  in  preference  to 
others. 

Q.  Why,  do  all  things  appear  BLACK  in  the 
DARK?  p.  371. 

A.  Because  there  is  no  light ;  and  as 
color  is  the  inherent  property  of  tight, 
therefore,  in  the  dark  all  thing's  are  with- 
out color. 

Of  course,  in  certain  degrees  of  darkness,  objects  are  ac- 
tually invisible.  The  question  refers  to  that  peculiar  de- 
gree of  darkness,  when  the  forms  of  objects  may  be  seen, 
but  not  their  hues. 

Q.  Why  are  the  FLAG-STONES  of  our  streets  fre- 
quently LOOSENED  after  a  FROST?  p.  326. 

A.  Because  the  moisture  beneath 
them,  expanded  during-  the  frost  and 
raised  the  flag-stones  from  their  beds ; 
but  afterwards,  the  moisture  thawed  and 


WARM    ROOMS.  397 

condensed  again,  leaving  the  flag-stones 
loose. 

Q.  Why  is  a  ROOM  WARMER,  when  the  win- 
dow CURTAINS  are  DRAWN?  p.  165. 

A.  Because  air  is  a  bad  conductor; 
and  the  air,  confined  between  the  cur- 
tains and  the  window,  opposes  both  the 
escape  of  warm  air  out  of  the  room,  and 
of  cold  air  into  the  room. 

Q.  Why  are  rooms  much  WARMER,  for  being 
furnished  with  DOUBLE  DOORS  and  WINDOWS?  p. 
165. 

A.  Because  air  is  a  bad  conductor  ; 
and  the  air  confined  between  the  double 
doors  and  windows,  opposes  both  the  es- 
cape of  warm  air  out  of  the  room  and  of 
cold  air  into  the  room. 

Q.  Why  is  LOOSE  clothing  WARMER  than 
that  which  fits  closely?  p.  165. 

A.  Because  air  is  a  bad  conductor ; 
and  the  quantity  of  air,  confined  between 
our  body  and  clothing,  prevents ;  1st — 
the  heat  of  our  body  from  escaping ;  and 
2dly — The  external  air  from  coming  in- 
to contact  with  our  body. 

Q.  Why  does  WETTING  a  CORNELIAN  make  it 
wore  TRANSPARENT?  p.  373. 

A.  Because  the  pores  of  the  corne- 
lian are  then  filled  with  icater ;  and  as 
the  density  of  the  mass  is  rendered  some- 


398  RUSTY    IRON — FIRES. 

what  more  uniform  than  when  those 
pores  were  filled  with  air,  the  stone  be- 
comes more  transparent. 

The  water  on  the  surface  of  the  stone  acts  also  as  a  var- 
nish, to  make  the  external  coating  more  lustrous. 

N.  B.  Transparency  depends  on  the  uniformity  of  parts. 
If  the  parts  of  any  substance  are  not  pretty  uniform,  the 
rays  of  light  are  refracted  and  absorbed  so  frequently,  that 
no  part  of  them  can  emerge  on  the  opposite  side. 

Q.       Why  does  IRON  rust  ? 

A.  Because  water  is  decomposed, 
when  it  comes  in  contact  with  the  sur- 
face of  iron  ;  and  the  oxygen  of  the  wa- 
ter combining1  with  iron  produces  an 
oxide,  which  is  generally  called  rust. 

N.  B.  Water  is  a  compound  of  Oxygen  and  Hydrogen, 
in  the  following  proportions :  8  Ibs.  of  oxygen,  and  1  Ib. 
of  hydrogen— 9  Ibs.  of  water. 

Q.  Why  does  PAINTING  iron  preve?it  it  from 
RUSTING  ?  p.  232. 

A.  Because  paint  prevents  the  moist 
air  from  coming  in  contact  with  the  iron. 

Q.  Why  is  a  dull  FIRE  REVIVED  by  sweeping 
clean  the  hobs,  bars,  ash-grate,  <fyc.  of  the  stove  ?  pp. 
52,  53. 

A.  Because  the  air,  which  was  ar- 
rested by  the  loose  dust  and  coals,  finds 
its  way  freely  to  the  fire,  so  soon  as  these 
obstacles  are  swept  away. 

N.  B.  The  brightness  of  a  fire  depends  on  its  supply  of 
oxygen,  derived  from  tlje  air. 

Q.  Why  does  STIRRING  a  dull  FIRE  serve  to 
quicken  it  ?  pp.  52,  53. 

A.     Because  it  breaks  up  the  clotted 


BREAD,    ETC.  399 

cinders  and  coals,  making-  a  passage  for 
the  air  into  the  very  heart  of  the  fire. 

A  fire  should  be  stirred  from  the  bottom,  and  not  from 
the  top. 

Q.  Why  does  SOAPY  WATER  "  lather  ?"  p. 
324. 

A.  Because  soap  makes  the  water 
tenacious,  and  prevents  its  bubbles  from 
bursting- ;  "  Lather"  is  only  an  accumu- 
lation of  bubbles. 

Q.  Why  is  well-made  BREAD  full  of  holes  or 
eyes  ?  p.  257. 

A.  Because  the  fermentation  of  the 
dough  throws  up  little  bubbles  filled  with 
carbonic  acid  gas ;  and  when  the  dough 
is  baked,  these  bubbles  are  made  perma- 
nent in  the  bread. 

Q.  Why  do  the  SAILS  of  a  WIND-MILL  turn 
round?  p.  108. 

A.  Because  the  wind,  blowing  against 
the  oblique  surface  of  the  sails,  pushes 
them  out  of  the  way,  driving  them  from 
place  to  place  in  a  restless  round. 

Q.  After  striking  a  finger-glass,  why  is  the 
SOUND  SILENCED,  upo?i  touching  the,  glass  with  your 
finger  ?  p.  378. 

A.  Because  the  pressure  of  your  fin-, 
ger  stops  the  vibrations  of  the  finger- 
glass  ;  and,  so  soon  as  the  finger-glass 
ceases  to  vibrate,  it  ceases  to  make  sound- 
waves in  the  air. 


400  STARS    TWINKLING. 

Q.  Why  does  a  WET  SPONGE  CLEAN  a  SLATE  ? 
11.321. 

A.  Because  the  water  of  the  wet 
sponge  dissolves  the  pencil  marks  made 
upon  the  slate. 

Something  is  due  to  the  mechanical  action  of  the  mere 
friction. 


Q.       Why  do  STARS  TWINKLE  more  than 
just  previous  to  RAIN  ?  p.  374. 

A.  1st  —  Because  the  air  is  unequally 
filled  with  vapor,  which  offers  constant 
obstructions  to  the  passage  of  the  rays  : 
and 

2dly  —  Because  clouds  and  other 
opaque  vapors  passing*  through  the  air, 
veil  for  a  little  time  the  light  of  the  stars, 
which  again  becomes  apparent  after  the 
clouds  have  passed  :  —  This  constant  shut- 
ting off  the  light  for  very  brief  intervals, 
produces  what  is  called  twinkling. 

The  answers  are  not  altogether  satisfactory  :  probably 
difraction  and  the  interference  of  different  rays  with  each 
other,  will  be  found,  at  some  future  time,  to  explain  the 
phenomenon  better. 

Q.  Why  does  MILK  BOIL  OVER  more  readily 
than  water  ?  p.  324. 

A.  Because  the  bubbles  of  milk,  pro- 
duced by  the  process  of  boiling,  are  more 
tenacious  than  the  bubbles  of  water  ;  and 
these  bubbles,  accumulating  and  climb- 


GLAZED    PICTURES,    ETC.  401 

ing   one    above    another,  soon    overtop 
the  rim  of  the  saucepan  and  run  over. 

Q.  If  a  PICTURE  be  GLAZED,  you  cannot  see  the 
"print"  in  certain  positions;  why  not?  p,  352. 

A.  1st — Because  glass  is  a  reflector ; 
and,  whenever  the  strong-  light  of  the 
sun  is  reflected  from  the  glass  to  the  eye 
of  the  spectator,  the  glass  becomes  in- 
tensely luminous,  and  the  picture  re- 
mains in  comparative  darkness  :  and 

2dly — When  the  spectator  is  so  placed, 
as  to  catch  the  rays  of  light  reflect- 
ed from  the  glass,  his  eye  is  dazzled 
with  the  strong  light,  and  cannot  see 
the  more  faintly  illuminated  picture  be- 
hind it. 

Q.  DUST  very  RARELY  flies  by  NIGHT  :  why 
is  this?  p.  188. 

A.  1st — Because  the  dews  of  night 
moisten  the  dust,  and  prevent  its  rising 
into  the  air :  and 

2dly — As  the  surface  of  the  earth  is 
colder  than  the  air  after  sunset,  the  cur- 
rent of  the  wind  will  incline  downward  ; 
and  tend  rather  to  press  the  dust  down 
than  to  buoy  it  up. 

Q.  When  the  cork  of  a  SODA-WATER  bottle  is 
drawn,  why  is  a  loud  REPORT  made  ?  p.  102. 

A.     Because  soda-water  contains  eight 


402  SODA-WATER    BOTTLES,    ETC. 

times  its  own  bulk  of  carbonic  acid  gas  ; 
which,  being-  suddenly  liberated,  strikes 
against  the  air,  and  produces  a  report. 

In  the  same  way,  as  when  we  strike  our  hand  upon  the 
table. 

Q.  Why  does  the  CORK  of  a  SODA-WATER  bottle 
FLY  OFF,  the  instant  it  has  been  released  from  the 
bond  ivhich  held  it  in  ?  p.  102. 

A.  Because  the  vast  quantity  of  car- 
bonic acid  gas  forced  into  the  soda-wa- 
ter can  no  longer  be  confined  ;  and  seek- 
ing to  escape,  drives  out  the  cork  with 
great  violence. 

Q.  Why  do  our  HANDS  and  LIPS  CHAP  in 
frosty  and  windy  weather  ?  p.  295. 

A.  1st — Because  the  wind  or  frost 
absorbs  the  moisture  from  the  surface 
of  the  skin  :  and 

2dly — The  action  of  wind  or  frost 
produces  a  kind  of  inflammation  on  the 
skin. 

Cold  acts  very  readily  upon  the  skin,  exciting  a  kind  of 
erysipelas,  of  a  red  color ;  if  the  cold  is  continued,  the 
skin  becomes  pale  and  languid,  and  the  patient  suffers 
from  chaps,  chilblains,  &c.  The  question,  however,  is 
one  belonging  to  the  physician,  rather  than  the  natural 
philosopher. 

Q.       When  a  BLACK  SUBSOIL  is  dug  or  ploughed 
'  up,  it  turns  of  a  reddish  BROWN  color  after  a  short 
time;  why  is  this?  p.  233. 

A.  Because  the  soil  contained  a  cer- 
tain compound  of  iron,  called  the  "pro- 


DECAYING   VEGETABLES.  403 

toxide"  which  is  black :  This  protoxide 
of  iron,  absorbing"  more  oxygen  from  the 
moist  air,  is  converted  into  another  com- 
pound, called  the  "  per-oxide  of  iron/' 
which  is  of  a  reddish  rusty  color. 

There  are  two  oxides  of  iron,  the  one  containing  more 
oxygen  than  the  other.  The  protoxide,  which  contains 
the  least  oxygen,  is  black;  the  peroxide,  which  contains  the 
most  oxygen,  is  red.  p.  394.  . 

Q.  Why  are  DECAYING  VEGETABLES  always 
WET?  p.  253. 

A.  Because  the  hydrogen  and  oxygen 
of  the  vegetables  are  given  up  by  decay, 
and  form  into  water. 

Water  is  composed  of  the  two  gases  oxygen  and  hydro- 
gen in  the  following  proportions :  8  Ibs.  of  oxygen  and  1  Ib. 
of  hydrogen  =  9  Ibs.  of  water. 

N.  B.  Deca}nng  vegetables  combine  into  the  following 
new  forms  :  1st,  The  oxygen  and  hydrogen  form  into  wa- 
ter :  and  2dly,  The  carbon  unites  with  the  oxygen  of  the 
air,  and  produces  carbonic  acid  gas. 

Q.  If  a  house  be  faced  with  STUCCO  to  resemble 
stone,  why  does  the  facing  very  often  FLAKE  OFF  in 
winter,  and  leave  the  house  unsightly  ?  p.  333. 

A.  Because  the  stucco  was  not  quite 
dry ;  therefore,  its  moisture  freezing-  and 
expanding1,  thrusts  the  stucco  away 
from  the  wall ;  and  when  the  thaw  sets 
in,  the  stucco  being*  unsupported,  will 
fall  by  its  own  weight. 

Q.  Why  do  the  LUSTRES  of  a  CHANDELIER  seem 
tinted  with  VARIOUS  brilliant  colors  ?  p.  364. 

A.  Because  each  "  drop"  of  the  chan- 


404  HORN — GLAZING    WINDOWS. 

delier  is  so  cut,  as  to  act  like  a  prism : 
It  decomposes  the  light,  and  reflects  the 
different  rays  thereof  from  its  different 
points  or  angles. 

Q.  HORN  is  TRANSPARENT,  why  are  NOT  horn 
SHAVINGS  transparent  also  ?  p.  373. 

A.  Because  the  surface  of  the  shav- 
ing has  been  torn  and  rendered  rough ; 
and  the  rays  of  light  are  too  much  reflect- 
ed and  refracted  by  the  rough  surface 
to  be  transmitted  through  the  shaving, 
so  as  to  produce  transparency. 

Q.  When  a  glazier  is  mending  a  window,  and 
cleans  the  pane  with  his  brush,  why  do  the  loose 
pieces  of  putty  (on  the  OPPOSITE  side  of  the  window- 
pane)  DANCE  up  and  down?  p.  142. 

A.  When  glass  is  rubbed,  electricity 
is  excited  in  the  parts  submitted  to  the 
friction,  and  on  the  part  opposite  also ; 
the  electricity  attracts  light  substances, 
such  as  loose  fragments  of  putty:  As 
soon  as  these  fragments  have  touched 
the  excited  part  of  the  glass  they  become 
charged,  and  fall  back  again ;  the  ledge 
on  which  they  fall  deprives  them  of  their 
burden,  and  they  then  fly  up  again  to 
receive  a  fresh  charge  :  This  process  be- 
ing repeated  often,  makes  the  commo- 
tion in  the  loose  fragments  of  putty,  re- 
ferred to  in  the  question. 


INDIAN    RUBBER.  405 

A  very  pretty  experiment  of  a  similar  kind  may  be  made 
thus :  Take  a  common  window  glass,  wipe  it  quite  dry 
and  warm,  and  support  it  on  two  wine  glasses  like  the 
slab  of  a  table :  Place  underneath  the  window  glass,  at  the 
distance  of  about  two  inches,  some  bran,  sand,  small  pieces 
of  paper,  Dutch  gold,  pith,  &c. :  If  you  now  rub  the  upper 
surface  of  the  window  glass  with  a  silk  rubber,  the  light 
substances  beneath  will  dance  up  and  down. 

N.  B.  The  rubber  may  be  made  thus:  Take  a  common 
cork  cut  evenly  and  flat,  cover  it  with  a  piece  of  silk,  and 
run  a  skewer  into  the  upper  surface  for  a  handle.  A  little 
amalgam  applied  to  the  rubber  will  greatly  improve  the 
experiment. 

Q.  When  you  rub  a  piece  of  paper  with  INDIAN 
RUBBER,  why  is  the  paper  sticky  ?  p.  34. 

A.  Because  the  friction  of  the  Indian 
rubber  against  the  surface  of  the  paper 
develops  electricity,  to  which  this  sticki- 
ness is  mainly  to  be  attributed. 

Q.  If  you  dry  a  piece  of  common  BROWN 
PAPER  by  the  fire  and  draw  it  once  or  twice  between 
your  two  KNEES,  why  will  it  STICK  fast  to  the  wall  ? 
p.  34. 

A.  Because  the  friction  develops 
electricity  on  the  paper,  which  manifests 
itself  by  this  property  of  adhesion. 

Q.  Why  can  noises  be  HEARD  (in  a  calm  day}  at 
a  GREATER  DISTANCE  on  the  sea  than  on  land  ?  ^.381. 

A.  1st — Because  the  air  over  the  sea 
is  generally  denser  and  more  laden  with 
moisture,  than  the  air  over  the  land  is : 
p.  139. 

2dly — The  density  is  more  uniform : 

.  380,  and 


406  MOUNTAINS — STARCH. 

3dly — Water  being-  more  elastic  than 
land,  is  a  better  propagator  of  sound. 

Q.  The  height  of  MOUNTAINS  may  be  ascer- 
tained by  a  BAROMETER  :  Explain  the  reason  of  this  ? 
p.  383. 

A.  As  we  ascend  a  high  mountain, 
the  quantity  of  air  above  us  becomes  less 
and  less  every  step  we  ascend,  and  re- 
quires less  mercury  to  balance  it ;  in  con- 
sequence of  which  the  mercury  in  the 
tube  of  the  barometer  falls. 

If  a  pile  of  books  be  placed  on  a  table,  the  bottom  book 
will  sustain  the  most  weight,  and  every  book  will  sustain 
less  and  less,  as  we  get  nearer  and  nearer  to  the  top :  The 
air  somewhat  resembles  this  pile.  That  on  the  surface  of 
the  earth  resembles  the  bottom  book  of  the  pile ;  and,  as  we 
ascend  a  mountain,  the  quantity  of  air  above  keeps  dimin- 
ishing, and  the  weight  to  be  sustained  is  in  proportion  less. 
'  For  general  practical  purposes  we  may  take  this  for  a 
rule :  for  every  100  feet  of  perpendicular  height,  the  ba- 
rometer will  fall  fa  of  an  inch.  If,  therefore,  the  barom- 
eter has  fallen  1J  inch,  you  know  the  mountain  is  1500 
feet  high. 

Q.       How  does  STARCH  assist  in  giving  a  smooth 

GLAZED  SURFACE  to  LINEN  1   p.  373. 

A.  It  fills  up  the  interstices  between 
the  threads;  and  makes  the  fabric  of 
more  uniform  density. 

"Interstices  between  the  threads." — Put  your  fingers 
close,  and  lay  your  open  hand  on  the  table— a  little  groove 
may  be  seen,  where  the  fingers  divide ;  these  grooves  may 
be  called  interstices;  and,  when  we  speak  of  the  "inter- 
stices of  linen,']  we  mean  the  groove  or  space  between 
thread  and  thread. 

Q.  If  a  DROP  of  WATER  be  spilt  on  a  table-cloth^ 
why  will  it  SPREAD  in  all  directions  ?  p.  75. 


SALT    MEAT.  407 

A.  Because  the  threads  of  the  cloth 
absorb  the  water  by  capillary  attraction. 

Q.       Why  does  SALT  PRESERVE  meat  ? 

A.  Because  it  removes  the  water  con- 
tained in  the  animal  fibre  :  absorbing  it, 
and  leaving-  the  meat  dry. 

The  reason  stated  above  is  not  the  sole  reason,  though 
it  is  certainly  the  chief  one.  The  following  have  some  in- 
fluence also : 

2.  Salt  is  composed  of  chlorine  and  sodium  ;  the  chlo- 
rine of  the  salt  takes  up  the  hydrogen  of  the  meat  as  it  is 
given  oft',  and  prevents  the  offensive  taste  and  smell  of  de- 
cay: 

3.  Brine  draws  away  the  albu'men  from  between  the 
muscular  fibres,  which  is  very  subject  to  putrefaction. 

4.  The  salt  unites  with  the  muscular  fibre,  and  makes  a 
new  chemical  compound,  much  less  subject  to  decay :  and 

6.  It  keeps  the  air  from  the  meat,  the  flies,  &c. 

Q.  Is  SALTED  meat  equally  nutritious  as  fresh 
meat  ? 

A.  No  :  Because  the  albumen  of  the 
meat  is  separated  from  the  flesh  by  the 
brine ;  as  well  as  the  alkaline  phosphates 
and  some  other  substances  of  great 
value. 

"Phosphates"  pronounce  fos'-fates.— Phosphates  are 
alkaline,  and  mineral. — ALKALINE  PHOSPHATES  are  phospho- 
ric acid  combined  with  some  alkali,  such  as  soda,  potash^ 
magnesia,  &c. 

"  Albu'men  of  the  meat " — a  substance  like  the  white  of 
an  egg,  which  lies  between  the  muscular  fibres  of  all  flesh, 
and  makes  the  meat  tender. 

"  The  alkaline  phosphates  of  meat "  are  such  as  these  : 
the  phosphate  of  soda,  the  phosphate  of  potash,  and  the 
phosphate  of  magnesia,  which  are  extracted  from  the 
meat  by  the  acid  re-action  of  the  brine. 


408  TOUGH    MEAT. 

Q.  Why  is  the  FLESH  of  OLD  animals  very 
TOUGH  ? 

A.  Because  it  contains  very  little  al- 
bu'menj  and  much  muscular  fibre. 

Q.  Why  is  MEAT  always  TOUGH,  if  it  be  put 
into  the  boiler  before  the  water  boils  ? 

A.  Because  the  water  is  not  hot 
enough  to  coagulate  the  albumen  be- 
tween the  muscular  fibres  of  the  meat, 
which  therefore  runs  into  the  water,  and 
rises  to  the  surface  as  a  scum. 

Q.  Why  is  MEAT  TOUGH,  which  has  been  BOILED 
TOO  LONG? 

A.  Because  the  albu'men  becomes 
hard,  like  the  white  of  a  hard  boiled 


The  best  way  of  boiling  meat  to  make  it  tender  is  this. 
Put  your  joint  in  very  brisk  boiling  water;  after  a  few 
minutes,  add  a  little  cold  water.  The  boiling  water  will 
fix  the  albu'men,  which  will  prevent  the  water  from  soak- 
ing into  the  meat  —  keep  all  the  juices  in  —  and  prevent  the 
muscular  fibre  from  contracting.  The  addition  of  cold 
water  will  secure  the  cooking  of  the  inside  of  the  joint,  as 
well  as  of  the  surface. 

Q.  Why  should  VEGETABLES  be  ALWAYS  eaten 
with  salted  meat  ? 

A.  Because  they  are  all  rich  in  POT- 
ASH, which  the  brine  has  deprived  the 
meat  of, 

Q.      Why  are  LAMB  and  VEAL  more  TENDER  than 

beef  and  mutton  ? 


MEAT.  409 

A.  Because  they  contain  more  albu'- 
men,  and  less  muscular  fibre, 

Albu'men  is  a  substance  like  the  white  of  an  egg. 
Q.       Why  do  LAMB  and  VEAL  TAINT  more  quickly 
than  beef  and  mutton  ? 

A.  Because  they  contain  a  large 
quantity  of  albu'inen,  which  is  very  liable 
to  undergo  putrefaction. 

Q.  Why  are  small  birds,  such  as  quails,  larks, 
partridges  j  fyc.,  covered  with  lard^  when  they  are 
roasted  ? 

A.  To  make  them  tender  and  savory. 
The  covering-  of  lard  prevents  the  savory 
constituents  of  the  bird  from  evapo- 
rating- with  the  water :  in  consequence 
of  which,  the  flesh  is  more  tender  and 
sapid. 

"  Sapid  "  i.  e.  full  of  flavor. 

Q.  Why  does  melted  WAX  become  HARD,  when 
told?  p.  109. 

A.  Because  the  particles  collapse; 
and,  being-  packed  more  closely  together, 
form  a  solid. 

The  sole  difference  between  a  liquid  and  a  solid  is  this — 
In  a  SOLID  the  particles  are  packed  more  closely  together, 
than  they  are  in  a  liquid.  The  tendency  of  heat  is,  to 
drive  the  particles  further  apart  from  each  other,  and  thus 
to  liquify  solids. 

Q.       Why  does  PAINT  often  BLISTER  from  heat  ? 

A.  Because  the  heat,  penetrating 
through  the  paint,  extracts  some  little 
moisture  from  the  wood,  and  turns  it  in- 
18 


410  ROTTING  LEAVES. 

to  vapor  or  steam.  As  this  vapor  re- 
quires room,  it  throws  up  blisters  in  the 
paint,  to  make  room  for  its  expanded 
bulk. 

Q.  Why  are  ROTTING  LEAVES  HOT  ?  pp.  60, 
253. 

A.  Because  the  fermentation  of  rot- 
ting* leaves  produces  carbonic  acid  gas, 
which  production  is  always  attended 
with  heat.  In  fact  rotting  is  a  species 
of  slow  combustion. 

N.  B. — The  carbon  of  the  leaves  unites  with  the  oxygen 
of  the  air,  to  produce  carbonic  acid  gas.  p.  259. 

The  new  combinations  disturb  latent  heat,  and  make  ifc 
sensible. 

Q.       Why  are  ROTTING  LEAVES  DAMP  ?  p.  253. 

Answered  before,  see  page  403. 

Q.  Why  does  BREAD  become  HARD,  after  it  has 
been  KEPT  a  few  days  ?  p.  153. 

A.  Because  the  vapor  and  gases  es- 
cape, leaving  the  solid  particles  dry  ;  so 
that  they  collapse,  and  become  more  sol- 
id and  hard. 

Q.       Why  is  NEW  BREAD  INDIGESTIBLE  ? 

A.  Because  the  change  called  "  pan'- 
ary  fermentation,"  is  not  completed. 

"  Panary  "  from  the  Latin  word  Panis  (bread) ;  "  panary 
fermentation  "  means,  the  fermentation  that  dough  under- 
goes in  order  to  become  bread. 

The  sugar  of  the  dough  is  converted  into  alcohol  and 
carbonic  acid  by  fermentation ;  the  dough  being  adhesive, 
prevents  the  escape  of  these  products,  till  the  mass  is 


PLANTS — OIL.  411 

baked;  when  the  gas  expands,  bursts  through  the  mass, 
leaving  a  number  of  holes  or  bladders,  to  show  where  it 
was  confined. 

So  long  as  the  bread  is  warm,  the  process  of  fermenta- 
tion is  going  on;  and,  therefore,  bread  should  never  be 
eaten,  till  it  is  24  hours  old. 

Q.  Why  are  PLANTS  WHITE,  which  are  kept  in 
the  DARK?  p.  372. 

A.  Because  chlo'rophyll  can  be  form- 
ed only  by  the  agency  of  the  sun's  rays ; 
and  it  is  this  peculiar  chemical  principle, 
which  gives  the  green  tinge ',  to  healthy 
leaves  and  plants. 

Chlo'rophyll  is  the  green  coloring  matter  of  leaves. 

Q.  WJiy  does  OIL  become  THICK  in  WINTER- 
TIME? p.  268. 

1st — Because  it  is  condensed  by  the 
cold,  and  rendered  more  solid  :  and 

2dly — Because  the  "  ste'arine,"  which 
is  held  in  solution  in  warm  weather,  is 
separated  by  the  action  of  the  cold  ;  and 
deposited  as  a  thick  white  almost-solid 
matter. 

"  Stearine  "  (from  the  Greek  word  o-reajj,  suet)  is  the  solid 
or  hard  ingredient  of  all  fat,  suet,  oil,  &c.  The  soft  or 
liquid  part  is  called  oleine  from  the  Latin  word  oleum  (oil.) 

Q.  Why  is  mutton  FAT,  Sfc,.,  solid,  and  OIL 
liquid  ? 

A.  Because  fat  contains  a  predomi- 
nance of  solid  ste'arine  ;  and  only  a  very 
small  quantity  of  the  liquid  oily  substance, 
called  oleine.  On  the  other  hand,  oil 


412          BUTTER RAILWAY  WHISTLE. 

contains  more  of  the  liquid  oleine,  and 
less  of  the  solid  matter,  called  ste'arine. 

Q.  Why  is  BUTTER  HARD  in  winter,  and  SOFT 
in  suMMER-tfme  ? 

A,  Because  in  winter-time  the  wea- 
ther is  too  cold  to  melt  the  ste'arine,  and 
the  butter  is  solid  ;  but  the  heat  of  sum- 
mer dissolves  it?  or  holds  it  in  solution 
in  the  oily  substance  called  oleine,  and 
the  butter  is  soft  and  liquid. 

Q.  Why  does  a  POP-GUN  make  a  loud  REPORT, 
when  the  paper  bullet  is  discharged  from  it.  ?  p.  1 02. 

A.  Because  the  air,  confined  between 
the  paper  bullet  and  the  discharging"  rod, 
is  suddenly  liberated,  and  strikes  against 
the  surrounding  air ;  this  makes  a  report 
in  the  same  way,  as  when  any  two  solids 
(such  as  your  hand  and  the  table)  come 
into  collision. 

Q.  How  does  STEAM  make  the  whistle  of  a  loco- 
motive engine  sound  ?  p.  11 0. 

A.  The  whistle  is  so  constructed,  as 
very  frequently  to  obstruct  the  free  pas- 
sage of  the  steam  through  the  jet;  in 
consequence  of  which,  very  rapid  vibra- 
tions are  caused  in  the  air,  producing  the 
sharp  shrill  sound  of  the  locomotive 
whistle. 

No  sound  is  ever  produced  in  any  sounding  body,  unless 
there  are  12£  vibrations  in  a  second  of  time ;  if  there  are 


SOUND — WOOD.  413 

7680  vibrations,  the  sound  is  sharp  and  shrill ;  the  shrill- 
ness increasing,  as  the  vibrations  increase  in  number. 

Q.  Why  will  BRIGHT  IRON  LOSE  its  POLISH  by 
being  put  into  a  FIRE  ?  p.  231. 

A.  Because  the  oxygen  of  the  air 
very  readily  unites  with  the  surface  of 
hot  iron,  and  forms  a  metallic  oxide ; 
which  displays  itself,  in  this  case,  by  a 
dull  leaden  color,  instead  of  a  red  rust. 

Q.  Why  does  SOUND  SEEM  LOUDER  in  CAVES, 
than  on  a  plain  ?  p.  381. 

A.  Because  the  sides  of  the  cave 
confine  the  sound-waves,  and  prevent 
their  spreading;  in  consequence  of 
which  their  strength  is  greatly  increased. 

Q.       Why  does  PAINT  PRESERVE  wood  ? 

A.  1st — Because  it  covers  the  sur- 
face of  the  wood,  and  prevents  both  air 
and  damp  from  penetrating1  into  the  pores : 

2dly — Because  paint  (especially  of  a 
white  color)  being*  a  bad  conductor,  pre- 
serves the  wood  of  a  more  uniform  tem- 
perature :  and 

3dly — Because  it  fills  up  the  pores  of 
the  wood,  prevents  insects  and  vermin 
from  harboring-  therein  and  eating1  up  the 
fibre. 

Q.  Why  does  UNSEASONED  WOOD  DECAY  much 
more  rapidly  than  wood  well  seasoned  ? 

A.     Because  the  albu'men  which  the 


414          ,  MOTHER    OP    PEARL. 

sap  contains,  produces  a  species  of  fer- 
mentation ;  during-  which,  the  cell'ulin 
and  ligneous  matter  of  the  wood  are 
turned  into  carbonic  acid  and  water. 

"  Albu'men,"  a  substance  resembling  the  white  of  an 

egg- 

u  Cellulin,"  the  substance  which  composes  the  cells  of 
wood,  as  wax  composes  the  cells  of  a  honey-comb  in  a 
bee- hive. 

"Ligneous  matter,"  or  vegetable  fibre,  is  the  hard  or 
woody  part  of  wood. 

Q.  Why  is  WOOD  placed  in  a  stream  of  run- 
ning WATER  tO  SEASON  it  ? 

A.  Because  the  running-  water  wash- 
es away  the  sap ;  and  thus  prevents  fer- 
mentation and  decay. 

Q.  Why  will  solutions  of  salts  PREVENT  the 
DECAY  of  wood  steeped  therein  ? 

A.  Because  the  salts  unite  with  the 
albu'rnen  of  the  sap,  coagulate  it,  and 
prevent  fermentation. 

Q.  Why  does  MOTHER  of  PEARL  show  so  many 
colors  ?  pp.  364,  370. 

A.  Mother  of  pearl  consists  of  a  vast 
number  of  very  thin  half-transparent  lay- 
ers of  unequal  thickness,  over-lapping 
each  other  like  the  scales  of  a  fish. 

Where  these  layers  terminate  are  very 
small  grooves  or  streaks  running  in  all 
directions,  which  act  like  prisms. 

It  is  these  streaJdngs  or  grooves,  which 


WATER    IN    A    GLASS.  415 

cause  the  various  and  changing-  colors  of 
mother  of  pearl. 

The  same  thing  may  very  easily  be  imitated,  and  is 
frequently  done  in  what  are  called  "iris  ornaments."  first 
invented  by  John  Barton,  Esq.,  of  the  Royal  Mint.  These 
iris  ornaments  are  made  of  steel,  and  have  about  30.000 
grooves  per  inch ;  they  are  used  in  court  dresses,  for  but- 
tons, sword  handles,  &c.,  and  are  very  brilliant  indeed. 

Mother  of  pearl  may  be  also  imitated  by  taking  impres- 
sions of  it  in  wax,  balsam  of  tolu,  isinglass,  or  gum  ;  these 
impressions  will  exhibit  all  the  shades  and  colors  of  mother 
of  pearl,  merely  because  the  impression  will  be  streaked 
or  grooved  in  a  similar  way. 

Q.  Why  can  you  fill  a  DRY  GLASS  BEYOND  the 
level  of  the  brim  ?  p.  206. 

A.  Because  the  mass  of  water  in  the 
glass  holds  the  overplus  back,  by  the 
power  of  attraction. 

Q.  Why  will  the  overplus  instantly  flow  over, 
if  the  edges  of  the  glass  are  wet  ? 

A.  Because  the  water  on  the  edge 
of  the  glass  has  an  affinity  to  the  water 
towering  above  it,  no  less  than  the  water 
in  the  body  of  the  glass  has  ;  and  in  this 
state  of  equilibrium  the  force  of  gravity, 
acting  on  the  elevated  particles  of  water, 
causes  them  at  once  to  fall  over. 

Q.  If  you  leave  a  little  tea  in  your  cup,  and 
rest  your  spoon  on  the  bottom  of  the  cup,  why  does  the 
TEA  RUSH  to  the  SPOON  ?  p.  387. 

A.  Because  the  spoon  attracts  it,  by 
what  is  called  capillary  attraction. 

The  sloping  spoon  makes  with  the  sides  or  bottom  of 
the  cup  a  space  in  the  shape  of  a  very  small  wedge ;  where 


416  LUCIFER    MATCHES. 

the  aperture  is  small,  the  cup  and  spoon  draw  the  tea  up . 
by  the  force  of  attraction ;  and  the  narrower  the  opening, 
the  stronger  the  attraction. 

Q.  When  LIQUOR  is  decanted  or  poured  from  a 
bottle,  why  does  it  GURGLE  ?  p.  256. 

A.  This  bubbling  noise  is  made  by 
the  air  bursting*  into  the  bottle,  and  the 
liquor  bursting-  out. 

The  liquor,  filling  the  neck  of  the  bottle,  prevents  the 
air  from  getting  freely  in ;  and  the  air,  pressing  against 
the  mouth  of  the  bottle,  prevents  the  liquor  from  getting 
freely  out:  in  consequence  of  which,  the  air  bursts  into 
the  neck  of  the  bottle,  and  the  liquor  runs  from  the  same, 
by  fits  and  starts,  as  either  is  able  to  prevail :  as  this  pro- 
cess is  repeated,  the  noise  produced  is  called  a  gurgle. 

Q.  Why  will  LUCIFER  MATCHES  IGNITE  by 
merely  drawing  them  across  any  rough  surface  / 
pp.  99,221. 

There  are  two  sorts  of  lucifer  matches ;  those  that  ignite 
silently,  and  those  that  ignite  with  an  explosion. 

A:  SILENT  LUCIFERS  are  made  of 
phosphorm,  which  has  an  affinity  to  oxy- 
gen at  the  lowest  temperature;  in- 
somuch that  the  little  additional  heat, 
caused  by  the  friction  of  the  match  across 
the  bottom  of  the  lucifer-box,  is  suffi- 
cient to  ig-nite  it ;  and,  at  the  same  time, 
to  ignite  the  sulphur  with  which  the 
match  is  tipped. 

EXPLOSIVE  LUCIFERS  are  made  of 
chlorate  of  potash,  which  will  explode  by 
very  slight  friction,  and  produce  combus- 
tion. 


MIRRORS.  417 

'"  Chlorate  of  potash  "  is  a  compound  of  chloric  acid 
and  potash.  Chloric  acid  is  a  compound  of  two  gases, 
chlorine  and  oxygen. 

Q.  Why  will  not  lucifer  matches  ignite,  if  they 
are  DAMP  ?  p.  48. 

A.  1st — Because  the  cold,  produced 
by  the  evaporation  of  the  water,  neutral- 
ises the  heat  produced  by  the  friction  of 
the  match  across  the  bottom  of  the  luci- 
fer-box :  and 

2dly — Because  the  damp  prevents  the 
free  accession  of  oxygen  to  the  match, 
without  which  it  cannot  burn. 

Q.  When  our  likeness  is  reflected  in  a  looking- 
glass,  the  entire  image  is  REVERSED;  so  that  our 
RIGHT  cheek  is  the  LEFT  cheek  of  the  reflection,  fyc.  ; 
why  is  this  ?  p.  345. 

If  a  person  stands  opposite  to  us,  his  position  in  ragard  to 
the  cardinal  points  of  the  compass  is  altogether  reversed. 

As  in  a  mirror  all  the  lines  and  angles 
of  incidence  equal  the  lines  and  angles  of 
reflection,  it  is  manifest  that  those  parts 
of  the  person  which  are  nearest  the  mir- 
ror, will  seem  to  be  nearer  than  those 
more  remote;  but,  if  our  right  cheek 
were  to  cross  over  to  the  right  cheek  of 
the  reflection,  then  this  law  would  be 
broken. 

Our  right  cheek  would  cross  over  to  the  right  cheek  in 
the  mirror,  and  our  left  to  the  left,  **XB  in  which  (with- 
out doubt)  the  extreme  points  of  the  diagonals  A  A,  and 
B  B,  are  further  apart  than  A  is  from  B. 
18* 


418  PAPER    CURLING,    ETC. 

Q  .  A  SILVER  tea-spoon  becomes  MORE  HEATED 
by  hot  tea,  than  one  of  INFERIOR  metal  (as  German 
silver,  Nickel,  fyc.);  why  is  this  ?  p.  156. 

A,  Because  silver  is  a  better  conduct- 
or than  German  silver  or  Nickel. 

The  three  best  conductors  of  heat  are,  1.  Gold,  2.  Silver, 
3.  Copper. 

Q.  If  you  scrape  a  slip  of  paper  with  a  knife^ 
why  will  the  PAPER  CURL  ? 

A.  Because  the  under  surface  of  the 
paper  is  contracted  by  the  scraping*,  which 
brings  the  particles  closer  together ;  this 
-contraction  of  the  under  surface  bends 
;the  slip  of  paper  into  a  curl  or  arch. 

Q.  Why  does  the  STOPPLE  of  a  decanter  STICK 
fast,  if  it  be  put  in  damp  ? 

A.  If  the  stopple  be  damp,  it  fits  the 
decanter  air-tight ;  and  if  the  decanter 
was  last  used  in  a  heated  room,  as  soon 
as  the  hot  air  inclosed  in  the  inside  has* 
been  condensed  by  the  cold,  the  weigh 
of  the  external  air  will  be  sufficient  to 
press  the  stopple  down,  and  make  it  stick 
fast. 

Q.  Why  does  the  STOPPLE  of  a  SMELLINGKBOT 
TLE  very  often  STICK  fast  ? 

A.     Because  the  contents  of  a  smell 
ing-bottle  are  very  volatile,  and  leave  the 
neck   of   the   bottle,   and    the   stopple 
damp. 

If  the  smelling-bottle  was  last  used  in 


DECAYING    VEGETABLES.  419 

a  hot  room,  as  soon  as  the  hot  air  and 
volatile  essence,  inside  the  bottle,  have 
been  condensed  by  the  cold,  the  weight 
of  the  external  air  will  be  sufficient  to 
press  the  stopple  down  and  make  it  stick. 

In  the  last  two  instances,  the  pressure  of  air  forces  the 
stopple  down  too  far,  so  that  it  is  like  a  cork  which  has 
been  forced  into  a  bottle :  Hence  there  are  two  mechani- 
cal forces  to  contend  against;  1st,  The  weight  of  air  on 
the  stopple  which  holds  it  down,  as  an  exhausted  receiver 
is  held  tight  on  the  plate  of  an  air-pump  :  and  2dly,  The 
neck  of  the  bottle,  (expanded  by  heat  when  the  stopple 
was  put  in.)  will  girt  it  with  great  pressure,  so  soon  as  it 
is  contracted  again  by  cold. 

Q.  Decaying  vegetables  are  first  of  a  brownish 
tint,  why  do  they  afterwards  turn  of  a  DEEP  BLACK? 

A.  Because  the  hydrogen  of  the  de- 
caying vegetables  is  separated  from  the 
mass  by  the  process  of  decay,  and  leaves 
a  larger  proportion  of  carbon  behind. 

Vegetable  fibre  contains    52 £  per  cent,  of  carbon. 
When  partially  decayed    54     "      "      "       " 
When  black  with  decay    56     "      "      "       " 

Q.  Why  is  an  OAK  STRUCK  by  LIGHTNING 
more  frequently  than  any  other  tree  ? 

A.  Because  the  grain  of  the  oak, 
being  closer  than  that  of  any  other  tree  of 
equal  bulk,  renders  it  a  better  conductor. 

It  is  said,  that  the  sap  of  the  oak  contains  a  large  quan- 
tity of  iron  in  solution,  which  impregnates  the  wood  and 
bark,  thus  increasing  its  conducting  power. 

Q.  Why  does  a  LOBSTER,  which  is  black  while 
alive,  turn  RED  by  being  BOILED  ? 

A.     The  blackness  is  due  to  a  peculiar 


420  BOILED    SHRIMPS,    ETC. 

coloring-  matter  secreted  by  the  lobster ; 
which,  however,  turns  red  when  exposed 
to  the  heat  of  boiling  water. 

Q.  Why  does  a  SHRIMP,  which  is  nearly  WHITE 
while  alive,  turn  RED  by  being  BOILED  ? 

A.  The  delicate  pinky  whiteness  is 
due  to  a  peculiar  coloring  matter  secre- 
ted by  the  shrimp ;  which,  however, 
turns  red  when  exposed  to  the  heat  of 
boiling  water. 

Many  coloring  matters  pass  into  each  other  under  very 
slight  changes  of  condition,  g.  e. 

Blue  indigo  changes  to  white  indigo,  if  only  one  atom 
more  of  hydrogen  be  added.  So  also,  the  green  chlorophyll 
of  leaves  changes  into  the  infinite  hues  of  the  petals  of 
flowers. 

The  science  of  colors  is  not  at  present  sufficiently  under- 
stood to  give  very  lucid  explanations  of  these  changes  ; 
the  facts  are  known,  and  little  else  besides. 

Q.  Why  is  the  SHADOW  of  the  MOON  stronger 
than  the  shadow  of  the  sun  ? 

A.  Because  the  light  of  the  moon  is 
not  so  strong  as  the  light  of  the  sun;  in 
consequence  of  which,  the  dispersed  and 
reflected  rays  of  the  moon  cannot  reduce 
the  opacity  of  shadows  so  much,  as  the 
more  intense  rays  of  dispersed  and  re- 
flected daylight. 

"  The  opa'city  of  shadows,"  i.  e.  the  darkness  of  shadows. 

Q.  Why  does  HARTSHORN  take  out  the  red  spot 
in  cloth,  produced  by  any  ACID  ? 

A.     Because  hartshorn  is  an  alkali; 


POWDERED    SULPHUR.  421 

and  the  peculiar  property  of  every  alkali 
is  to  neutralize  acids. 

"  Alkali "  pronounce  Al'-ka-li.  Soda,  potash,  magnesia, 
&c.,  are  alkalies. 

Upon  this  principle  effervescing  drinks  are  made  of  a 
carbonate  of  soda  (an  alkali),  and  citric  or  tartaric  acid. 
Effervescence  is  produced,  by  the  giving  off  of  carbonic 
acid  during  the  process  of  neutralization. 

N.  B. — The  carbonic  acid  is  made  from  the  carbon  (of 
the  carbonate  of  soda)  combining  with  the  oxygen  of  the 
acid.  p.  43. 

,.     Q.       Why   will  POWDERED   SULPHUR   QUENCH 
\FIRE  more  readily  than  water  ? 

A.  1st — Because  powdered  sulphur 
has  a  very  strong-  affinity  for  oxygen,  and 
converts  it  into  sulphurous  add ;  as  this 
is  the  case,  the  fire  is  deprived  of 
its  essential  food  (oxygen),  and  is,  in 
fact,  starved  out :  and 

2dly — Because  sulphurous  acid  throws 
off  dense  white  fumes,  and  surrounds  the 
fire  with  an  extinguishing  atmosphere. 

The  difference  between  sulphurous  acid  and  sulphuric 
acid  is  this :  sulphurous  acid  contains  less  oxygen  than 
sulphuric  acid.  When  we  burn  sulphur  in  air,  it  throws 
off  suffocating  white  fumes,  called  sulphurous  acid. 

Q.      How  does  STARCH  STIFFEN  linen  1 

A.  By  filling  the  interstices  of  the 
fabric  with  a  solution  of  starch,  by  which 
means  the  linen  is  made  more  rigid. 

Q.  Why  should  LIGHTNING-CONDUCTORS  be 
POINTED  ? 

A.     Because  points  conduct  electricity 


422  BRICKS — POTATOES,    ETC. 

away  silently  and  imperceptibly :  but 
knobs  produce  an  explosion,  which  would 
endanger  the  building. 

Points  empty  the  clouds  of  electricity,  acting  at  a  much 
greater  distance  than  knobs  ;  thus  a  Leyden  jar  of  consid- 
erable size  may  be  safely  and  silently  discharged,  by  hold- 
ing the  point  of  a  needle  an  inch  or  two  off. 

Blades  of  grass,  the  ears  of  corn,  and  other  pointed  ob- 
jects, serve  to  empty  the  clouds  of  their  electricity. 

Q.  Why*  do  BRICKS  turn  GREEN,  after  they 
have  been  exposed  to  the  weather  ? 

A.  The  "  green"  is  a  moss  or  lichen, 
which  grows  on  the  bricks  ;  the  seeds  of 
which  were  carried  to  the  surface  by  the 
winds. 

Q.  When  POTATOES  are  boiled,  why  are  those 
at  the  TOP  of  the  boiler  COOKED  SOONER  than  those 
nearer  the  fire  ? 

A.  1st — Because  the  hottest  particles 
of  the  water  rise  to  the  top  of  the  boiler, 
and  the  coldest  particles  sink  to  the  bot- 
tom :  and 

2dly — Because  the  top  of  the  boiler  is 
always  enveloped  with  very  hot  escap- 
ing steam  ;  in  consequence  of  which,  the 
potatoes  on  the  top  are  subjected  to  more 
intense  heat,  than  those  at  the  bottom  of 
the  boiler  are. 

Q.  If  a  SILVER  SPOON,  which  has  been  tarnished 
by  an  EGG,  be  rubbed  with  a  little  SALT,  why  will  the 
tarnish  disappear  ? 

A.     The  tarnish  in  this  case  is  sulphw- 


SOTJR    MILK,    ETC.  423 

ret  of  silver,  produced  by  the  sulphur  of 
the  egg  combining  with  the  silver  spoon. 
Salt  acts  upon  this  sulphuret  of  silver 
thus — 

The  sodium  of  the  salt  combines  with 
the  sulphur,  and  produces  sulphate  of  so- 
da. The  sulphur  being  thus  taken  away 
from  the  silver,  the  tarnish  disappears. 

"  Sulphuret  of  silver,"  i.  e.  sulphur  in  combination  with 
silver. 

Salt  is  a  compound  of  the  metal  called  sodium,  and  the 
gas  called  chlorine. 

"  Sulphate  of  soda"  is  a  combination  of  sulphuric  acid 
and  soda. 

Q.       Why   are    BOOKS   discolored    by   AGE   or 

DAMP  1 

A.  Because  the  fibre  of  the  paper 
becomes  partially  decomposed,  and  va- 
rious impurities  from  the  atmosphere  (or 
other  sources)  become  mixed  with  it. 

Q.       Why  does  SOUR  MILK  CURDLE  ? 

A.  Milk  consists  of  five  ingredients : 
1,  Casein  or  curd  ;  2,  Butter ;  3,  Sugar; 
4,  Water ;  5,  Certain  Salts. 

The  Ca'sein  or  curd  of  sweet  milk  is 
like  the  white  of  an  egg  before  it  is 
boiled ;  but  the  casein  or  curd  of  sour 
milk  is  like  the  white  of  an  egg  after  it 
is  boiled. 

This  casein  or  curd  of  milk  is  coagu- 
lated by  acids : — When  milk  is  sour,  the 


424  MILK    SOUR. 

lactic  add  of  the  sour  milk,  mixing-  with 
the  casein,  coagulates  it ;  in  consequence 
of  which,  it  separates  from  the  water, 
and  becomes  an  insoluble  mass ;  or  (in- 
other  words)  the  milk  curdles. 

"  Lactic  acid  "  (from  the  Latin  word  Lac,  milk)is  the  acid 
of  sour  milk.  But  it  is  found  in  several  other  substances 
also,  as  in  the  fermented  juice  of  beet- root,  turnips,  car- 
rots, rice-water,  tanning  bark,  &c. 

Q.       Why  does  MILK  turn  SOUR  by  KEEPING? 

A.  Because  it  undergoes  a  fermen- 
tation ;  during*  which  "  lactic  acid"  is 
formed,  which  turns  the  milk  sour. 

The  lactic  acid  is  formed  from  the  sugar  of  milk  by  fer- 
mentation. 

Q.  Why  does  MILK  turn  SOUR  in  HOT  weather, 
much  sooner  than  in  cold  ? 

A.  Because  heat  very  greatly  accel- 
erates the  process  of  fermentation  ;  dur- 
ing* which  lactic  acid  is  formed,  which 
turns  the  milk  sour. 

Q.  Why  can  you  NEVER  BOIL  STALE  MILK 
without  curdling  it  ? 

A.  Because  stale  milk  is  in  an  incip- 
ient state  of  fermentation,  which  the  heat 
of  the  fire  greatly  accelerates  :  The  lac- 
tic acid  which  is  formed  during*  fermen- 
tation, mixing*  with  the  casein  of  the 
milk,  coagulates  it. 

Casein  (  pronounce  cas'-e-in)  is  the  curd  of  milk,  coagu- 
lated by  adds  only. 

Q.       Why  does  RENNET  CURDLE  MILK  ? 


CREAM,    ETC.  425 

A.  Because  it  converts  the  sugar  of 
milk  into  lactic  acid,  which  mixes  with 
the  casein  and  coagulates  it. 

Milk  contains  soda  and  potash ;  so  long  as  these  alkalies 
are  combined  with  the  casein  of  the  milk,  the  compound 
is  soluble  in  water,  and  the  milk  sweet :  but  when  the 
acid  deprives  the  casein  of  the  alkalies  by  combining  with 
them  itself,  then  the  casein  is  no  longer  soluble  in  water, 
but  is  precipitated  or  curdled. 

Rennet  is  the  prepared  inner  membrane  of  the  stomach 
of  a  calf;  so  called  from  the  German  word  rinnen  (to 
curdle.) 

Q.       Why  does  CHURNING  cream  convert  it  into 

BUTTER  ? 

A.  Cream  is  the  fat  or  butter  of 
milk,  contained  in  little  globular  cases  of 
albu'men : 

By  churning,  this  film  or  envelop 
of  albu'men  is  broken,  and  the  butter  or 
.  fat  set  free. 

The  globules  are  invisible  to  the  naked  eye,  but  may  be 
distinctly  seen  floating  about  milk,  by  a  tolerable  micro- 
scope. 

Albu'men  is  a  substance  resembling  the  white  of  an  egg. 

Q.       Why  does  the  SUN  or  fire  WARP  WOOD  ? 

A.  Because  heat  draws  out  the  moist- 
ure from  that  part  of  the  wood  which 
faces  it,  and  causes  the  heated  surface 
to  shrink ;  as,  therefore,  the  heated  sur- 
face of  the  wood  shrinks,  and  is  smaller 
than  the  other  surface,  it  draws  it  into  a 
curve,  and  the  wood  is  warped. 

Q.  Why  does  the  SUN,  for  the  most  part,  FADE 
artificial  COLORS  ? 


426  KNIVES — DOUGH. 

A.  Generally,  the  loss  of  color  arises 
from  tlie  oxidation  of  the  substances  used 
in  dyeing  ;  as  tarnish  and  rust  are  an  oxi- 
dation of  metals. 

Sometimes,  however,  the  ingredients 
of  the  dye  are  otherwise  decomposed  by 
the  sun ;  and  the  color  (which  is  due  to 
a  combination  of  ingredients)  undergoes 
a  change,  as  soon  as  the  sun  deranges 
or  destroys  that  combination. 

Q.  Wlien  a  KNIFE  is  sharpened  on  a  GRIND- 
STONE, why  is  OIL  or  water  used  ? 

A.  To  make  the  contact  more  perfect. 
The  oil  or  water  fills  up  the  interstices 
of  the  rough  stone,  and  makes  a  more 
uniform  surface :  In  consequence  of 
which,  the  entire  edge  of  the  blade  is  sub- 
mitted to  an  equal  portion  of  friction, 
which  would  otherwise  be  rough  and 
uneven. 

Q  Why  does  BAKING  dough  convert  it  into 
BREAD  ? 

A.  When  flour  is  baked  in  an  oven 
its  starch  is  changed  into  a  gum  called 
dextrin :  and 

A  similar  change  is  produced  upon 
the  farinaceous  portion  of  the  dough. 
The  yeast  (added  to  the  dough)  converts 
part  of  the  starch  and  sugar  into  alcohol 


MOULDY    BREAD.         .  427 

and  carbonic  acid  :  Of  these,  the  alcohol 
evaporates  in  the  oven,  and  the  carbonic 
acid  forces  the  dough  into  bubbles,  in  its 
effort  to  escape,  rendering-  the  bread 
light  and  full  of  eyes. 

In  100  Ibs.  of  bread,  and  100  Ibs.  of  dough,  we  have 

STARCH.       SUGAR.     DEXTRIN. 

In  dough,  68  Ibs.  5  Ibs.  0=100 

In  bread,  63*"  3}  "  18=100 

whereby  it  will  be  seen  that  16£  Ibs  of  starch  have  been 
converted  into  the  gum  called  dextrin  by  baking. 

Dextrin  is  a  gummy  matter  similar  to  that  which  com- 

Eoses  the  cells  of  wood  (called  cellu'lin),  only  it  is  soluble 
i  cold  water. 

Diastase  (pronounce  di-as'-tase)  is  a  peculiar  vegetable 
principle  of  malt  extracted  by  water,  which  converts  starch 
into  dextrin  or  sugar. 

Q.  Why  does  BREAD  become  mouldy,  after  it 
has  been  KEPT  a  few  days  ? 

A.  Because  spores  of  the  mould  fun- 
gus, floating  in  the  air,  fix  themselves  in 
the  decaying  bread  and  germinate. 

Fungi  germinate  only  in  decaying  bodies. 

Spores  (one  syllable)  or  Sporules  (two  syls.*)  from  the 
Greek  word  airopa  (seed}  is  a  word  used  by  botanists  to  in- 
dicate the  seed  of  cryptogamic  or  flowerless  plants.  They 
differ  from  seeds  in  this  respect,  every  part  of  the  spore 
shoots  into  a  plant,  and  not  one  particular  point  alone,  as 
in  common  seeds. 

Q.  Why  does  MEAT  PUTREFY  sooner  in  hot, 
DAMP  weather,  than  in  cold  ? 

Putrefaction  is  simply  the  decomposition  of  the  original 
elements,  and  their  reunion  in  a  new  order.  The  new  order 
is  as  follows : 

1st.  Carbon  and  oxygen  unite  to  form  carbonic  acid ; 
2dly.  Hydrogen  and  oxygen  "    "     "         water; 
3dly.  Hydrogen  and  nitrogen    "      "      ammonia. 
N.  B. — Carbon  unites  with  oxygen  with  a  readiness  pro- 


428  PUTRID    MEAT. 

portioned  to  its  heat :  When  red  hot,  the  combination  is 
most  readily  effected. 

The  reason  why  meat  taints  more 
rapidly  in  hot  weather  than  cold,  is  this ; 
Because  the  carbon  of  the  meat  unites 
with  the  oxygen  of  the  air  more  readily 
when  hot  than  cold :  and 

The  reason  why  damp  aids  putrefac- 
tion is  this  ;  Because  the  damp,  deposit- 
ed on  the  surface  of  the  meat,  is  of 
itself  one  of  the  compounds  of  putrefac- 
tion, and  leaves  an  excess  of  hydrogen 
in  the  meat :  and 

Thus  the  original  proportions  and  com- 
binations of  the  meat  are  altered  and  de- 
composed. 

The  chief  reason  why  salt  preserves  meat  is  because  it 
absorbs  the  water  from  it,  and  deprives  it  of  hydrogen. 

Q.  Why  does  MEAT  PUTREFY  most  rapidly  in 
very  CHANGEABLE  weather  ? 

A.  Because  moisture  is  more  freely 
deposited  on  the  meat  in  very  change- 
able weather;  and  this  moisture  is  a 
chief  compound  of  putrefaction. 

Q.  BIRDS,  after  they  are  killed,  KEEP  longer  m 
their  FEATHERS,  than  when  they  are  plucked ;  why  is 
this  ? 

A.  Because  the  feathers  prevent  the 
air  or  damp  from  getting  so  readily  to 
the  bird,  to  produce  fermentation  or  de- 
cay. 


PLANTS — INDIAN-RUBBER.  429 

Q.       Why  do  PLANTS,  which  are  kept  on  a  ivin- 

,  BEND  tO  the  GLASS  ? 

A.  Because  the  side  away  from  the 
light  grows  faster,  than  the  side  facing 
the  light,  and  pushes  the  top  of  the  plant 
over  in  a  curve. 

Wood  is  warped  by  the  fire,  because  the  under  surface  is 
smaller  than  the  upper. 

And  paper  is  made  to  curl  by  scraping  the  under  surface 
with  a  knife  for  the  same  reason. 

N.  B. — Woody  tissue  is  deposited  in  the  stem  most 
abundantly  on  the  side  nearest  the  light ;  and  where  wood 
is  formed  most,  growth  is  slowest,  because  the  part  is  less 
succulent. 

Q.  Why  does  INDIAN-RUBBER  erase  PENCIL 
MARKS  from  paper  ? 

A.  Indian-rubber  contains  a  very 
large  quantity  of  carbon  :  Black-lead  is 
carbon  and  iron. 

Now,  the  carbon  of  the  Indian-rubber 
has  so  great  an  attraction  for  the  black- 
lead,  that  it  takes  up  the  loose  traces  of 
it  left  on  paper  by  a  pencil. 

Q.  Why  does  WATER  ROT  WOOD  ?  and  why 
does  AIR  rot  WOOD  ? 

A.  Because  it  converts  the  solid  part 
of  the  wood  into  what  is  called  humuSj 
by  oxidation  ;  thus — 

1st — The  carbon  of  the  wood  is  oxi- 
dised into  carbonic  acid  ;  and 

2dly — The  hydrogen  of  the'  wood  is 
oxidised  into  water — the  residue  be- 
comes humus  or  mould. 


430  WATER — HOT   IRON. 

"  Humus,"  pronowice  U'-mus.  The  black  mould  of  our 
gardens  is  called  humus,  and  is  produced  by  the  decay  of 
vegetable  matter  by  the  action  of  air  and  water. 

Q.  Why  does  WATER  make  a  HISSING  noise, 
when  it  is  poured  on  FIRE  ? 

A.  Because  the  part  which  comes  in 
contact  with  the  hot  coals  is  immediately 
converted  into  steam;  and,  as  it  flies  up- 
ward, meets  other  particles  of  water  not 
yet  vaporised ;  the  collision  produces 
very  rapid  vibrations  in  the  air,  and  a 
hissing1  noise  is  the  result. 

Q.  Why  does  HOT  IRON  make  a  hissing  noise, 
when  plunged  into  WATER  ? 

A.  Because  the  hot  iron  converts  into 
steam  the  particles  of  water,  which  come 
in  immediate  contact  with  it;  and,  as 
the  steam  flies  upwards,  it  passes  by 
other  particles  of  water  not  yet  vapo- 
rised :  tt}e  collision  produces  very  rapid 
vibrations  in  the  air,  and  a  hissing  noise 
is  the  result. 

Q.  Why  will  HOT  IRON  BEND  more  easily  than 
cold? 

A.  Because  it  is  not  so  solid.  The 
particles  are  driven  further  apart  by  heat, 
and  the  attraction  of  cohesion  weakened  ; 
in  consequence  of  which,  the  particles 
can  be  made  to  move  on  each  other  more 
readily. 

By  a  still  further  application  of  heat,  the  particles  will 


HEATED   IRON,   ETC.  431  , 

be  driven  so  far  asunder  from  each  other,  that  the  solid 
iron  will  liquefy :  in  which  state  the  particles  will  move  on 
each  other  almost  without  resistance. 

Q.       Why  does  IRON  turn  first  RED  and  then 

WHITE  from  HEAT  ? 

A.  Light  and  heat  depend  upon  vi- 
brations ;  the  more  rapid  the  vibrations, 
the  more  intense  the  light  and  heat ; 
White  heat  is  a  more  intense  degree  of 
heat  than  red,  and  occurs  only  when  the 
vibrations  are  most  rapid. 

Candescence  occurs  when  bodies  are  heated  to  800°. 
It  begins  with  a  dull  red  color,  passes  to  an  orange  tint, 
and  ultimately  to  a  shining  white. 

The  more  perfect  the  combustion  of  carbon  the  whiter 
its  color. 

Probably  these  varying  colors  depend  upon  some  variety 
in  the  thickness  of  the  molecules  of  the  heated  substance, 
caused  by  the  influence  of  heat ;  whereby  it  is  made  to 
reflect  different  colors  according  to  the  varying  thickness 
of  the  molecules.  But  the  subject  is  not  well  understood 
at  present. 

Molecules  (pronounce  mo'-le-cules)  are  very  small  par- 
ticles of  matter  in  a  mass.  ATOMS  have  no  regard  to 
aggregation. 

Q.  Why  does  WATER  FREEZE  more  quickly 
than  MILK? 

A.  Because  milk  contains  salts  in  so- 
lution ;  in  consequence  of  which,  it  re- 
quires a  greater  degree  of  cold  to  con- 
geal it  than  water.  >C 

Water  freezes  at  32°,  but  salt  and  water  will  not  freeze 
unless  the  thermometer  sinks  below  7°. 

Q.  Why  does  HOT  WATER  FREEZE  more  quickly 
than  cold  ? 

A.     Because  there  is  a  slight  agitation 


432  OIL — FREEZING   WATER. 

on  the  surface  of  hot  water,  which  pro- 
motes congelation ;  by  assisting-  the 
crystals  to  change  their  positions,  till  they 
take  up  that  which  is  most  favorable  to 
their  solidification. 

Other  causes  may  have  a  minor  influence,  as  for  example : 
In  hot  water,  the  particles  are  subdivided  into  smaller 
globules  by  the  heat,  and  offer  less  resistance  to  the  action 
of  cold  than  larger  ones.  2dly.  The  air  has  been  expelled 
from  the  water  by  the  process  of  boiling — hence  the  In- 
dians always  used  boiled  water  in  their  ice-pits. 

N.  B. — Air  must  be  expelled  from  water  before  it  can  be 
frozen. 

Q.  Why  will  a  little  OIL  on  the  surface  of 
water  prevent  its  FREEZING  ? 

A.  Because  oil  is  a  bad  conductor, 
and  prevents  heat  from  leaving*  the  wa- 
ter. 

The  surface  of  water  never  freezes,  till  the  whole  mass 
is  cooled  down  to  42°. 

Q.  Why  does  water  in  a  very  EXPOSED  place 
freeze  more  rapidly  than  that  which  is  under  cover, 
or  in  places  less  exposed  ? 

A.  1st — Because  evaporation  goes  on 
more  rapidly,  when  water  is  exposed ; 
and  carries  away  heat  from  the  general 
mass:  and 

2dly — Any  covering  will  radiate  heat 
into  the  water  'below,  and  prevent  the 
mass  from  cooling  down  to  42°. 

"Radiate  heat"  means,  to  send  heat  out  in  rays. 

Q.  Why  are  GLUE,  GUM,  STARCH,  and  PASTE, 
adhesive  ? 


RAIL-WAY   TRAIN,    ETC.  433 

A.  Because  the  water  used  with 
them  rapidly  evaporates,  and  leaves  them 
solid. 

They  lose  their  adhesiveness  when  dissolved  in  water ; 
and,  therefore,  must  always  be  suffered  to  become  dry, 
before  they  will  hold  with  tenacity. 

Q.  Why  does  a  rail-way  TRAIN  make  more 
NOISE,  when  It  passes  over  a  BRIDGE  or  MEADOW, 
than  when  it  runs  over  SOLID  GROUND  ? 

A.  Because  the  bridge  (or  meadow) 
is  very  elastic,  and  vibrates  much  more 
from  the  weight  of  the  train,  than  the 
solid  earth ;  in  consequence  of  which,  it 
produces  more  definite  sound-waves. 

The  bridge  acts  as  a  sounding-board ;  and  the  water  or 
earth,  below  the  bridge,  repeats  the  sound. 

Q.  Why  does  MILK  BOIL  more  QUICKLY  than 
water  ? 

A.  Because  less  steam  is  carried  off 
from  the  thick  liquid  (milk),  than  from 
the  thin  liquid  (water)  ;  in  consequence 
of  which,  the  heat  of  the  whole  mass  rises 
more  quickly. 

Q.  Why  will  MILK  BURN  very  easily,  when 
boiled,  while  water  will  not  do  so  ? 

A.  1st — Because  milk  contains  solid 
organic  substances,  capable  of  burning ; 
which  water  does  not : — and 

2dly — Because  the  heat  of  the  fire 
coagulates  the  albu'men  of  the  milk 
19 


«jfe* 
434  WAX — STEEL,    ETC. 

which  falls  to  the  bottom,  and  adheres 
to  the  boiler. 

Albu'men  is  a  substance  resembling  the  white  of  an  egg-. 
Q.       Why  does  WAX  become  SOFT,  before  it  turns 
LIQUID  ? 

A.  Because  it  absorbs  heat  sufficient 
to  loosen  the  contact  of  its  particles, 
before  it  has  absorbed  sufficient  to  liquefy 
the  mass. 

Q.  If  you  heat  STEEL  RED  HOT  in  the  fire,  and 
then  plunge  it  suddenly  into  cold  water,  it  becomes 
HARD  and  BRITTLE  j  why  is  this  ? 

A.  Because  the  sudden  chill  violently 
expels  the  latent  heat,  which  would 
have  settled  in  the  steel,  had  it  been  al- 
lowed to  cool  slowly. 

The  malleability  and  toughness  of  metals  depend  upon 
their  power  of  absorbing  heat. 

Q.  Why  are  the  ICE-PITS  of  India  lined  with 
straw  and  coarse  blanketing — stopped  up  with  STRAW 
at  the  mouth,  instead  of  a  door — and  THATCHED  on 
the  roof,  instead  of  being  covered  with  slates  or  tiles  ? 

A.  Because  straw  and  coarse  blank- 
eting, being*  very  bad  conductors  indeed, 
prevent  the  external  heat  from  getting 
to  the  ice-pits  to  dissolve  the  ice. 

Q.  How  do  the  natives  of  INDIA  provide  them- 
selves with  ICE,  when  the  temperature  is  much  higher 
than  the  freezing  point  ? 

A.  They  make  a  hole  in  the  earth 
about  2  feet  deep,  and  30  feet  square : 
They  cover  the  bottom  of  this  hole,  to 


WARM    COUNTRIES,    ETC.  435 

the  depth  of  a  foot,  with  the  stalks  of 
Indian  corn  or  sugar-canes : 

On  this  bed  they  place  fleet  unglazed 
earthern  pans  about  an  inch  and  a  quar- 
ter deep,  and  pour  into  them  (at  sun-set) 
soft  water,  which  has  been  boiled  and 
suffered  to  cool.  At  sun-rise  the  water 
is  found  to  be  frozen,  and  is  thrown  into 
the  ice-pit. 

The  reason  of  this  is  :  The  vessels  being  porous,  part  of 
the  water  evaporates  through  the  pans,  and  reduces  the 
heat  of  the  water  sufficient  for  congelation. 

Q.  Why  is  it  customary,  in  very  HOT  COUN- 
TRIES, to  sit  in  rooms  separated  by  CURTAINS,  instead 
of  walls ;  and  to  keep  these  curtains  constantly 
sprinkled  with  WATER  1 

A.  Because  curtains  are  bad  conduct- 
ors of  heat ;  and  the  rapid  evaporation 
of  water  reduces  the  temperature  of  the 
room  10  or  15  degrees. 

Q.  Why  is  it  impossible  to  WRITE  on  GREASY 
PAPER  ? 

A.  Because  grease  has  no  affinity  for 
water  or  ink,  and,  therefore,  will  not  mix 
with  it. 

Q.  Why  is  rain  said  to  "  bring  down  the 
cold  ?" 

A.  Because  the  change  in  the  atmos- 
phere, which  causes  rain  ,to  fall,  sets  free 
latent  heat,  and  makes  it  sensible. 


436  TURPENTINE,    ETC. 

Frost  is  broken  up  by  the  rains ;  and  the  sharp,  piercing 
wind,  being  laden  with  vapor,  is  much  mitigated. 

Q.  Why  does  TURPENTINE  take  out  GREASE 
spots  from  doth  ? 

A.     Because  it  dissolves  fixed  oils. 

The  fixed  oils  are  all  greasy  oils,  such  as  sperm  oil,  olivo 
oil,  &/C.  The  other  sort  of  oils,  called  volatile  or  essential 
oils,  are  those  used  in  perfumery,  &c. 

Q.       Why  does  OXALIC  acid  take  out  INK  spots  ? 

A.  Because  it  dissolves  the  tannate  of 
iron,  of  which  the  black  portion  of  the 
ink  consists. 

"  Tannate  of  iron  "  is  tannic  acid  combined  with  iron. 
Tannic  acid  is  the  acid  of  tan,  or  oak  bark. 

Q.  When  COPPER  is  exposed  to  moist  air,  it  is 
incrusted  with  a  green  coating ,  called  VERDIGRIS  ; 
why  is  this  ? 

A.  Because  the  oxygen  of  the  moist 
air  combines  with  the  copper,  and  forms 
what  is  called  a  hydrate  of  the  carbonate 
of  the  protoxide  of  copper. 

"  Protoxide  "  (wpwroj-oxide,  the  lowest  or  first  state  of 
oxidation) :  The  protoxide  of  copper  is  a  combination  of 
one  portion  of  oxygen,  and  one  of  copper.  Hydrate  (from 
the  Greek  word  v<$wp,  water)  is  a  compound  containing 
water ;  but  in  all  hydrates,  the  substance  forms  so  inti- 
mate a  union  with  water,  as  to  solidify  it,  and  render  it  a 
component  part.  A  "  hydrate  of  the  carbonate  of  copper," 
is  a  compound  of  water,  carbonic  acid,  and  copper;  and 
"  A  hydrate  of  the  carbonate  of  the  protoxide  of  copper," 
is  copper  in  its  lowest  state  of  oxidation,  in  which  carbonic 
acid  and  water  is  so  united,  as  to  form  a  solid. 

Q.       Why  does  ZINC  TARNISH  id  the  air  ? 

A.  Because  the  oxygen  of  the  moist 
air  combines  with  the  zinc,  and  forms  an 
oxide  of  zinc. 


SALT — SILVER.  437 

An  "  oxide  of  zinc  "  is  oxygen  in  union  with  zinc. 
Q.       WJiy  does  SALT  turn  silver  BLACK  ? 

A.  Because  it  precipitates  an  oxide 
of  silver  on  the  surface  of  the  spoon,  the 
color  of  which  is  black. 

"  Marking  ink"  is  made  of  soda  and  the  nitrate  of  sil- 
ver ;  the  black  mark  being  due  to  the  oxide,  precipitated 
on  the  cloth. 

Q.  How  can  the  BLACK  stain  of  SILVER,  made 
by  salt)  be  REMOVED  ? 

A.  By  washing*  the  silver  in  harts- 
horn, or  common  ammonia ;  by  which 
means,  the  oxide  will  be  re-dissolved 
and  the  blackness  entirely  disappear. 

Q.       Why  does  WAXING  cotton  or  thread  make  it 

STRONGER  ? 

A.  Because  it  cements  the  loose  fila- 
ments to  the  cord  ;  and  makes  the  strands 
of  the  thread  more  compact. 

The  "  filaments  of  the  cotton,"  are  the  loose  fibres  hang- 
ing about  it.  The  "  strands  "  are  the  twists  or  single  yarns 
twisted  into  a  thread.  Sewing  cotton  contains  two,  three, 
and  occasionally  more  than  three  strands. 

Q.  The  cromb  of  walking-sticks  is  made  by 
BOILING  the  end  of  the  stick,  and  then  bending  it 
into  an  arch;  why  is  a  STICK  made  FLEXIBLE  by 
BOILING? 

A.  Wood  contains  many  substances 
soluble  in  hot  water,  as  starch,  sug*ar, 
glim,  &c.,  and  several  other  substances 
which  are  softened  by  it :  as,  therefore, 
several  substances  are  dissolved,  and 


438  MANURE— GUANO. 

others  softened  by  boiling  water,  the  stick 
is  rendered  flexible. 

Cell'ular  fibre  and  woody  matter,  when  boiled  in  water, 
become  soft  and  gelatinous. 

Q.  Explain  how  MANURE  makes  LAND  FER- 
TILE. 

A.  As  plants  extract  a  certain  amount 
of  salts  from  the  soil,  which  are  entirely 
removed  at  harvest,  it  is  obvious  that  the 
soil  will  become  gradually  impoverished, 
unless  these  matters  are  restored ;  this 
restoration  is  made  by  manuring  the 
soil. 

Q.       Why  is  GUANO  valuable  as  a  MANURE  ? 

A.  Because  it  contains  nitrogen  and 
ammonia,  both  of  which  are  essential  to 
plants. 

Q.       What  is  the  use  of  LIME,  MARL,   $c.:  as 

MANURE  ? 

A.  1st — They  decompose  vegetable 
substances :  and 

2dly — They  liberate  the-  alkalies  in 
union  with  the  silica  of  the  soil. 

Silica  (pronounce  SilM-cah),  from  the  Latin  word  Silex, 
flint — one  of  the  most  common  substances  on  the  earth- 
containing  the  following  varieties — white  chuckystone—- 
violet  amethysts— red  quartz— yellow  cairngorum— Brazil 
pebbles  for  spectacle  glasses — rock  crystal — chalcedony — 
agate — blood-stones—cornelian — flint,  &c. 

Q.  Why  do  you  see  the  reflection  of  TWO  can- 
dles, or  two  fires,  in  a  looking-glass  or  window-pane, 
though  there  is  only  ONE  candle  or  fire  in  the  room  ? 

A.     Because  each  surface  of  the  look- 


SKY    BLUE — LIGHT.  439 

ing-glass  or  window-pane  makes  a  reflec- 
tion. 

N.  B.— In  order  to  see  these  two  reflections,  you  must 
not  stand  directly  before  the  glass,  but  a  little  on" one  side. 

Q.  Why  is  the  SKY  BLUE  on  a  fine  day,  and, 
not  red  or  orange  ? 

A.  Because  the  momentum  of  red  and 
orange  rays  (being1  greater  than  that  of 
blue)  causes  them  to  penetrate  beyond 
the  clouds  ;  but  the  blue  rays  are  stop- 
ped on  their  passage,  and  reflected. 

Q.  Why  is  it  LIGHT  when  the  heavens  are 
covered  with  thick  CLOUDS  1 

A.  Because  the  multiplied  reflections 
of  the  sun  in  the  atmosphere  are  suffi- 
cient to  give  light  upon  the  earth,  even 
when  thick  clouds  are  passing1  over  the 
disc  of  the  sun. 

Q.       Why  are  putrefying  FISH  LUMINOUS  ?  p.  266. 

A.  Because  the  carbon  of  the  fish, 
uniting*  with  oxygen,  forms  carbonic  acid ; 
and  the  phosphoric  acid  of  the  fish  (be- 
ing thus  deprived  of  oxygen)  is  con- 
verted into  phosphorus :  as  soon  as  this  is 
the  case,  the  phosphorus  begins  to  unite 
with  the  oxygen  of  the  air,  and  becomes 
luminous. 

Carbonic  acid  is  a  compound  of  carbon  and  oxygen. 

Phosphoric  acid  is  a  compound  of  phosphorus  and  oxy- 
gen. If  you  take  the  oxygen  away  from  phosphoric  acid, 
the  residue,  of  course,  is  phosphorus. 


440  SEA    LUMINOUS. 

The  luminousness  spoken  of  is  due  to  the  slow  combus- 
tion of  the  phosphorus,  while  it  is  uniting  with  the  oxygen 
of  the  air. 

Q.  Why  is  the  SEA  often  LUMINOUS  in  summer- 
time ?  p.  266. 

A.  Because  the  small  jelly  fish  decay ; 
the  phosphoric  acid  which  they  contain 
(being*  deprived  of  oxygen)  is  converted 
into  phosphorus,  unites  with  the  oxygen 
of  the  air,  and  becomes  luminous. 

Q.  What  causes  the  disease  commonly  called 
the  itch  ? 

A.  It  is  produced  by  an  insect  called 
the  "  itch  insect,"  which  burrows  in  the 
skin,  and  is  greatly  encouraged  by  filth. 
Sulphur,  corrosive  sublimate,  &c.,  will 
destroy  the  insect,  and  cure  the  disease. 

Corrosive  sublimate  is  made  of  200  parts  of  mercury 
with  72  of  chlorine.  It  is  plain  to  see  how  the  disease  is 
contagious. 

Q.  Why  does  the  use  of  SALT  BEEF  produce 
scurvy  ? 

A.  Because  the  soluble  salts  are  re- 
moved from  the  beef  by  brine :  in  con- 
sequence of  which,  it  cannot  restore  to 
the  human  system  those  salts,  which  are 
essential  to  preserve  the  blood  in  a 
healthy  state. 

Q.  Why  is  LIME-JUICE  a  perfect  CURE  for 
SCURVY  ? 

A.     Because  it  contains  the  very  salts, 


VEGETABLES  —  WOOD.  441 

removed  from  the  beef  by  the  action  of 
brine. 

Namdy  —  alkaline  phosphate  —  and  sulphate,  chloride 
and  phosphate  of  lime. 

"Alkaline  phosphates"  are  such  as  these  —  phosphate 
of  soda,  phosphate  of  potash,  and  phosphate  of  magnesia; 
i.  e.  soda,  potash,  or  magnesia,  in  combination  with  phos- 
phoric acid. 

"  Sulphate  of  lime,"  a  compound  of  sulphuric  acid  and 
lime. 

"  Chloride  of  lime,"  a  compound  of  chlorine  gas  and 
lime. 

"  Phosphate  of  lime,"  a  compound  of  phosphoric  acid 
and  lime. 


Q.       Iftniy  does  the  use  of  VEGETABLES  generally 

PREVENT  SCURVY  ? 

A.  Because  they  contain  the  soluble 
salts  removed  from  the  beef  by  brine  ; 
which  being1  restored  by  the  vegetables, 
preserve  the  blood  in  a  healthy  state. 

Why  does  WOOD  DECAY  ? 

A.  Because  the  oxygen  of  the  air 
unites  with  the  carbon  and  hydrogen  of 
the  wood,  and  forms  carbonic  acid  and 
water. 

Q.  When  WINE  is  spilt  on  a  TABLE-CLOTH, 
napkin,  or  handkerchief,  how  can  the  STAIN  be 

REMOVED  ? 

A.  By  dipping*  it  in  a  weak  solution 
of  chlorine. 

^  Bleaching  powder  is  only  lime  impregnated  with  chlo- 


rine. 


Q.      When  WINE  is  spilt  on  a  tabk-cloth, 
19* 


442  INFECTIOUS    DISEASES. 

why  do  persons  generally  cover  the  part  immediately 
with  SALT  ? 

A.  Because  salt  is  a  compound  of 
chlorine  and  sodium ;  and  the  chlorine  of 
the  salts  acts  as  a  bleaching  powder. 

Q.  When  INFECTIOUS  DISEASES  prevail,  how 
can  the  contagious  matter  be  removed  from  bed-rooms, 
hospitals,  houses,  fyc.  ? 

A.  By  using-  a  solution  of  chlorine,  or 
of  sulphurous  acid  ;  which  will  not  only 
remove  the  contagious  matter,  but  also 
the  offensive  smell  of  a  sick  room. 

Q.  What  is  an  excellent  remedy  against  RATS 
and  MICE  ? 

A.  Sulphuretted  hydrogen.  All  that 
is  necessary  is  to  introduce  the  beak  of  a 
retort  into  a  rat-hole,  while  sulphuretted 
hydrogen  is  being  given  off. 

It  will  destroy  the  rats  and  make  the  hole  unfit  for 
others  to  frequent. 

Sulphuretted  hydrogen  is  made  thus.  Put  into  a  retort 
or  glass  bottle  a  quantity  of  sulphuret  of  iron,  prepared  by 
heating  a  rod  of  iron  red  hot ;  bring  it  in  contact  with  a  roll 
of  sulphur — allow  the  sulphuret  of  iron  formed  to  drop 
into  water;  pour  over  it  a  small  portion  of  water,  and 
then  add  an  equal  quantity  of  sulphuric  acid ;  sulphuretted 
hydrogen  will  be  given  off  most  copiously. 

Q.       Why  does  GUNPOWDER  EXPLODE? 

A.  Because  of  the  instantaneous  pro- 
duction and  expansion  of  carbonic  acid, 
sulphurous  acid,  and  nitrogen. 

Gunpowder  consists  of  76  parts  of  nitre,  13  charcoal, 
and  11  sulphur. 


SHADE,    ETC.  443 

Q.  An  object  in  the  SHADE  is  not  so  bright 
and  apparent,  as  an  object  in  the  sun ;  why  is  it 
not? 

A.  Because  objects  in  the  shade  are 
seen  by  reflected  light  reflected,  i.  e.  the 
light  is  twice  reflected  :  and,  as  the  rays 
of  light  are  always  absorbed  in  some 
measure  by  every  substance  on  which 
they  fall,  therefore,  some  light  is  lost ; 
1st — Before  the  second  reflection  is  made, 
and  2cily — In  the  object  that  makes  the 
second  reflection : 

Part  of  the  rays  are  absorbed,  and  part  are  scattered  in 
all  directions  by  irregular  reflections ;  so  that  rarely  more 
than  half  is  reflected,  even  from  the  most  polished  rnetals. 

Q.  Why  are  GREEN  GOOSEBERRIES,  CURRANTS, 
<^c.,  HARD  ;  and  RIPE  ones  SOFT  ? 

A.  Because  they  contain  an  infinite 
number  of  little  cells,  with  thick  walls ; 
these  become  thinner  from  day  to  day, 
as  the  fruit  ripens,  until  they  break ;  when 
the  fruit  becomes  soft. 

Q.  Why  is  PORTER  much  DARKER  than  ale  or 
beer  ? 

A.  Because  the  malt  of  which  porter 
is  made  is  dried  at  a  higher  temperature 
and  slightly  charred. 

Small  beer  is  a  weak  wort  fermented,  and  contains  1£ 
per  cent,  of  alcohol. 

Ale  is  a  stronger  wort,  and  contains  7  per  cent,  of  alcohol. 
Porter  contains  4£  per  cent,  of  alcohol. 
Brown  stout  contains  6|  per  cent,  of  alcohol. 
Burton  ale  contains  8i  per  cent,  of  alcohol. 


444  WINE HAMS,    ETC. 

Q.  7f  WINE  or  BEER  be  imperfectly  corked,  why 
does  it  rapidly  turn  sour  ? 

A.  Because  air  gets  into  the  liquor  ; 
and  the  oxygen  of  the  air,  combining 
with  the  alcohol  of  the  liquor,  produces 
ace'tic  acid. 

1  alcohol  and  4  oxygen,  become  1  hydrous  acetic  acid 
and  2  water. 

Q.  Why  does  pyroligneous  acid  PRESERVE 
MEAT  and  remove  its  taint  ? 

(Pyroligneous  acid,  is  vinegar  extracted  from  wood.) 

A.  Because  it  contains  a  small  quan- 
tity of  creasote,  which  is  a  great  preser- 
vative of  all  animal  substances. 

Creasote,  pronounce  Cre-a-sote  (from  two  Greek  words, 
*f)«aj,  flesh,  and  <ro>£<u,  /  save),  an  extract  from  the  oil  of  tar, 
and  a  powerful  antiseptic. 

Q.  Why  are  HAMS  preserved  by  SMOKING 
them  ? 

A.  Because  the  smoke  of  a  wood  fire 
contains  creasote,  which  is  a  great  pre- 
servative of  all  animal  substances. 

Q.      Is  TEA  a  NUTRITIOUS  beverage  ? 

A.  Yes;  the  tea-leaf  contains  the 
largest  amount  of  nutritive  matter  of  any 
plant  used  as  human  food ;  though  only 
a  portion  is  extracted  by  our  common 
method  of  making  tea.  When  soda  is 
added,  the  casein  of  the  leaves  is  dissolved, 
and  the  nutritive  quality  of  the  tea  is 
much  increased. 


SOAP,    ETC.  445 

Casein  pronounce  Cas'-e-in,  from  the  Latin  word  caseus, 
cheese;  because  cheese  consists  chiefly  of  the  casein  of 
milk.  It  is  found  in  many  vegetable  substances,  as  peas, 
beans,  lentils,  &c.,  and  is  the  same  as  the  substance  called 
legu'mine. 

Q.  How  do  the  Tartar  tribes  make  a  most 
nutritious  food  from  tea  ? 

A.  They  boil  the  leaves  with  soda, 
and  eat  them  with  salt  and  butter. 

Q.  SOAP  is  made  of  oil  or  fat.  How  is  it 
that  oil  and  fat  make  water  greasy,  whereas  SOAP 
destroys  grease  ? 

A.  Oil  contains  two  parts ;  the  solid 
part  called  stearine^  and  the  liquid  part 
called  oleine. 

Stearine  of  oil  is  not  soluble  in  water ; 
but  when  soda  or  potash  is  boiled  with 
it,  the  oily  principle  flies  off,  and  the 
stearine  is  converted  into  an  oxide  of 
potassium,  which  is  quite  soluble  in  wa- 
ter. 

Stearine  (pronounce  Ste'-a-rine),  from  the  Greek  word 
o-rsap,  suet;  the  acid  of  stearine  unites  with  the  soda  or 
potash,  and  the  oily  principle  called  glycerine  flies  off. 

Oxide  of  potassium  is  the  fundamental  part  of  potash ;  it 
is  what  chemists  call  a  metallic  oxide. 

Q.  What  is  the  difference  in  composition  between 
HARD  soap  and  SOFT  SOAP  ? 

A.     The  hard  soaps  are  made  of  soda, 
and  the  soft  soaps  are  made  of  potash. 
Q.       Why  is  sorrel  sour  ? 
A.     Because  it  contains  oxalic  acid. 

Oxalic,  from  the  Greek  word  o|aXis,  sorrel.  Oxalic  acid 
is  sometimes  erroneously  called  "  salt  ofkmons" 


446  APPLES — VINEGAR. 

Q.  Why  are  unripe  APPLES,  GOOSEBERRIES, 
and  RHUBARB,  SOUR. 

A.     Because  they  contain  malic  acid. 

Ma'lic,  from  the  Latin  word  malum,  an  apple. 

Q.  Why  are  tamarinds  and  unripe  GRAPES 
so ur  ? 

A.  Because  they  contain  tartaric 
acid. 

Tartaric  acid  is  the  acid  of  tartar.  Tartar  is  a  substance 
deposited  by  wine;  adhering,  like  a  hard  crust,  to  the 
sides  of  the  casks. 

Q.       Why  does  TANNING  hides  convert  them  into 

LEATHER  ? 

A.  Because  oak  bark  contains  tannic 
acid ;  and,  on  evaporation,  this  acid  pre- 
cipitates a  solution  of  glue  upon  the 
hides,  which  converts  them  into  leather. 

Q.       Why  are  citrons,  limes,  LEMONS,  and  unripe 

ORANGES,  SOUR  ? 

A.     Because  they  contain  citric  acid. 

Citric,  from  the  Latin  word  citrus,  a  kmon  or  citron. 
Q.       Why  is  VINEGAR  SOUR  ? 

A.     Because  it  contains  ace'tic  acid. 

Ace'tic,  from  the  Saxon  word  aeced,  vinegar ;  whence 
also  acid,  i.  e.  like  vinegar. 

Q.  Why  do  old  WINE-CASKS  SMELL  OFFEN- 
SIVELY ? 

A.  Because  wine  (and  whiskey)  con- 
tain an  acid  called  oenanthic  acid  ;  which 
unites  with  the  alcohol  of  the  wine,  and 
forms  a  salt  of  an  offensive  smell. 


CANDLES — TEETH.  447 

This  salt  is  called  the  oenanthate  of  ethyle,  i.  e.  the 
winey  acid  of  ether. 

(Enanthate,  from  the  Greek  word  011/05,  wine;  and 
"ethyle,"  from  the  two  Greek  words,  atQrip-v\ii,  the  basis 
or  fundamental  principle  of  ether. 

Q.  When  a  CANDLE  is  BLOWN  OUT,  whence 
arises  the  OFFENSIVE  ODOR  ? 

A.  The  tallow  distills  a  substance  in 
the  smoke,  called  acryle,  which  has  a 
very  offensive  smell. 

"  Acryle  "  (pronounce  ac'-ryle)  from  two  Greek  words, 
aKprj-vXij,  tlje  basis  or  principle  of  a  wick  or  end,  i.  e.  the 
odor  which  issues  from  a  wick-end,  after  it  has  been 
blown  out. 

Q.       What  causes  the  decay  of  teeth  ? 

A.  After  the  enamel  is  worn  off,  the 
dentine  or  ivory  of  the  tooth  is  left  bare  : 
This  dentine  or  ivory  is  full  of  little  tubes, 
filled  with  lime  ;  Now,  the  acids  of  saliva, 
mucus,  and  food,  dissolve  this  lime,  and 
fill  the  tubes  with  foreign  matters  ;  after 
which,  the  tubes  dissolve  or  crumble 
away,  leave  the  nerve  exposed,  and  the 
pain  of  tooth-ache  ensues. 

Dentine  (from  the  Latin  word  dens,  a  tooth)  is  the  main 
part  of  the  tooth. 

Q.       Why  does  CREASOTE  CURE  TOOTH- ACHE  ? 

A.  Creasote  acts  as  a  caustic,  and 
burns  away  the  mortified  bone,  or  ulcer 
formed  upon  it,  which  produced  the 
pain.  r*fl'.'. 

Tooth-ache  arises  from  numerous  causes,  as  cold, 
stomach,  caries,  or  decay,  &c.  Creasote  is  a  remedy  for 
tooth-ache  only  when  the  pain  arises  from  caries. 


448  INDIAN    RUBBER,    ETC. 

Ca'-jri-es  is  a  Latin  word  which  signifies,  mortification  or 
ulcer  of  the  bone. 

Q.       What  is  Indian  rubber  ? 

A.  The  oil  or  resin  from  various 
species  of  ficus,  oxidised  in  contact  with 
air. 

"  Fi'-cus,"  the  fig-tribe. 

Q.       What  is  gutta  percha  ? 

A.  The  oil  or  resin  of  a  tree  which 
grows  in  Malacca  (Asia),  called  Isonan- 
dra  gutta,  oxidised  in  contact  with  air. 

Q.  What  wines  contain  the  MOST  spirit,  and 
what  the  least  ? 

A.  Champagne  is  one  of  the  weakest 
wines,  then  hock,  then  claret,  then  sherry, 
and  port  is  one  of  the  most  potent. 
Four  glasses  of  port  being  nearly  equal 
to  five  glasses  of  sherry. 

Champagne  contains  about  12  per  cent,  of  alcohol. 
Hock  "       "          13 

Claret  "       "  16 

Sherry  19 

Port  "       "          23* 

Q.  What  is  the  origin  of  the  term  PROOF 
spirit  ? 

A.  It  is  derived  from  the  old  method 
of  testing  spirit,  which  was  thus  :  the 
spirit  to  be  tested  was  poured  over  gun- 
powder, and  ignited  ;  if  the  powder  ex- 
ploded, the  spirit  was  said  to  be  above 
proof;  if  it  did  not  explode,  it  was  said 
to  be  below  proof. 


STEEL — MARKING    INK.  449 

Q.  What  do  we  mean^  at  the  present  day,  by 
spirit  above  and  below  PROOF  ? 

A.  If  we  say  that  spirit  is  10  over 
proof,  we  mean  this — that  100  gallons  of 
it  will  require  10  gallons  of  water  to  re- 
duce the  spirit  to  proof  strength.  So  on 
the  converse,  if  we  say  that  spirit  is  10 
under  proof,  we  mean  that  10  gallons  of 
water  must  be  taken  from  the  spirit  to 
raise  it. to  proof  strength. 

Proof  spirit  has  .91833  specific  gravity;  the  strength  of 
spirit  is  now  tested  by  an  instrument  called  an  hydrometer. 

Q.      How  is  STEEL  made  from  IRON  ? 

A.  The  iron  is  surrounded  with  char- 
coal, and  placed  for  six  or  eight  days  in  a 
furnace,  intensely  heated ;  the  carbon 
unites  with  the  iron,  and  forms  what  is 
called  "  carburet  of  iron"  (or  steel). 

Q.       What  is  meant  by  "  SHEAR  STEEL  ?" 

A.  Steel  used  for  making  shea?*s\  for 
dressing  woollen  cloth :  Shear  steel  is 
broken  and  welded  frequently. 

Welded,  i.  e.  hammered  together  again. 

Q.       What  is  common  MARKING  INK  ? 

A.  There  are  generally  two  bottles — 
one  containing  a  solution  of  the  carbon- 
ate of  soda :  arid  another  containing  a 
solution  of  nitrate  of  silver.  The  cloth 
is  first  moistened  with  the  carbonate  of 
soda,  dried,  and  then  written  on  with  a 


450 

q 

pen  'dipped  in  the  nitrate  of  silver.  An 
oxide  of  silver  is  thus  precipitated,  and 
leaves  a  black  mark  behind. 

Q.       What  is  JEWELLER'S  GOLD  ? 

A.  An  alloy  of  gold  and  copper  with 
silver — this  gold  is  liable  to  tarnish,  but 
its  brilliancy  can  easily  be  restored,  by 
immersing  the  metal  in  ammonia. 

Q.         HOW  is  IRON  GALVANIZED  ? 

A.  By  plunging  it  into  melted  zinc  ; 
when  an  alloy  is  formed  on  the  surface, 
which  prevents  oxidation. 

Q.  What  is  the  difference  between  LEAD  and 
SOLDER  ? 

A.  Solder  is  a  mixture  of  lead  and 
tin. 

Fine  solder  is  2  tin  and  1  lead. 
Coarse  solder  is  1  tin  and  4  lead. 

Q.       What  is  WHITE  LEAD,  used  for  paint  ? 

A.  It  is  prepared  by  placing  sheets 
of  lead  over  earthen  pots,  which  contain 
weak  acetic  acid,  and  stand  upon  tan  or 
dung.  The  lead,  being  corroded  with 
the  acid,  unites  with  the  carbon  and 
oxygen  evolved  from  the  dung. 

Q.       What  is  PEWTER  ? 

A.  An  alloy  of  lead  (or  bismuth)  and 
tin. 

In  the  following  proportions :  1  part  lead  and  20  parts 
tin. 


TIN — FIREWORKS.  451 

Q.       What  is  BLOCK  -BEN  1 

A.  Tin  purified  by  heat,  and  run  into 
moulds,  which  form  blocks  of  great 
size. 

Some  3  cwt.,  and  some  even  more. 

Q.  How  is  the  GREEN  FIRE  of  fireworks  pro- 
duced ? 

A.  By  the  nitrate  of  bary'tes,  which 
burns  with  a  green  hue. 

(Barytes,  pronounce  ba-ry'-tes)  an  earth  so  called  from  a 
Greek  word  which  signifies  heavy,  (/?apt>?.)  It  is  mado 
thus;  100  parts  of  nitrate  of  bary'tes  well  dried,  9  of  sul- 
phur, 7  of  chlorate  of  potash,  2  charcoal,  4  sulphuret  of 
antimony,  all  well  dried  and  mixed  in  a  mortar. 

Q.  How  is  the  RED  FIRE  of  fireworks  pro- 
duced ? 

A.  By  the  nitrate  ofstroritian,  which 
burns  with  a  red  hue. 

(Stron'tian  is  an  earth,  so  called  from  a  village  in 
Argyleshire  of  the  same  name,  where  it  was  first  dis- 
covered.) It  is  made  thus ;  100  parts  of  dry  nitrate  of 
stron'tian,  mixed  with  12  parts  of  chlorate  of  potash,  30 
sulphur,  10  sulphuret  of  antimony,  and  3  charcoal,  all 
dried  and  rubbed  carefully  in  a  mortar. 

N.  B. — Unless  care  be  taken  the  mixture  will  explode. 


452  POISONS. 


ANTIDOTES  FOR  POISONS. 

Q.  If  a  person  has  swallowed  a  MINERAL 
poison,  suck  as  ARSENIC,  what  is  the  best  antidote  ? 

A.  A  tea-spoonful  of  sulphur — or  half 
a  tea-spoonful  of  pearl-ash — or  a  ivine- 
glass  of  soap-suds  : 

After  a  little  while,  give  a  table-spoon- 
ful of  antimonial  wine,  and  plenty  of 
warm  water. 

Q.  If  a  person  has  swallowed  a  VEGETABLE 
poison,  such  as  SULPHURIC  ACID,  AQUA-FORTIS,  or 
OXALIC  ACID,  what  is  the  best  antidote  ? 

A.  Lime,  chalk,  pearl-ash,  magnesia, 
carbonate  of  soda,  or  soap-suds,  and  a 
plenty  of  warm  water ;  a  dessert-spoonful 
of  antimonial  wine  should  be  added,  if 
at  hand. 

The  chalk  or  lime,  &c.,  unites  with  the  oxalic  acid,  and 
forms  oxalate  of  lime,  which  is  quite  innocuous. 

Q.  If  LAUDANUM  has  been  taken,  what  is  the 
best  antidote  ? 

A.  A  tea-spoonful  of  common  mus- 
tard ;  and  to  keep  the  patient  walking. 

Q.  If  CHLORINE  has  been  taken,  what  is  the 
best  antidote  ? 

A.  Ammonia,  which  will  neutralize 
the  ill  effects  of  chlorine. 

Q.  If  IODINE  has  been  taken  in  too  large  a 
quantity ',  what  is  the  best  antidote  ? 


ANTIDOTES    FOR    POISON.  453 

A.  Iron-filings  are  the  best  antidote 
for  an  over-dose  of  iodine. 

Q.  If  a  person  feels  faint  from  the  fumes  of 
PRUSSIC  ACID,  what  is  the  best  antidote  ? 

A.  To  smell  the  vapors  of  strong  am- 
monia^  which  will  soon  restore  con- 
sciousness. 

Q.      How  can  WARTS,  <^c.,  be  REMOVED  1 

A.  By  rubbing1  them  with  common 
solid  potash. 

Q.       What  is  the  best  antidote  to  VERDIGRIS  ? 

A.     Sugar,  or  white  of  egg. 

Q.       What  is  the  best  antidote  to  CORROSIVE 

SUBLIMATE  ? 

A.  White  of  egg1,  or  milk  ;  which  will 
combine  with  them,  and  neutralize  their 
poisonous  qualities. 

Q.  If  a  person  has  eaten  too  much  FRUIT,  what 
is  the  best  antidote  ? 

A.  Lime,  chalk,  pearl-ash,  magnesia, 
carbonate  of  soda,  or  soap-suds. 

Great  relief  is  often  found  by  eating  the  hard  part  of 
cheese  (cut  close  to  the  rind)  thickly  covered  with  com- 
mon salt ;  the  reason  is  plain. 


GLOSSARY. 


Acetic     Acid.         called 

Citric        "  " 

Nitric        "  " 

Oxalic       "  " 
Sulphuric  " 

Sulph.  of  Alumina  " 
Lime 
Iron 

Copper  " 

Magnesia  " 

Soda  " 
Zinc 

Nitrate  of  Potash  " 


Prussiate  of  Potash 
Tartrate  of  Potash 
Acetate  of  Copper 
Muriate  of  Soda 
Oxide  of  Lead 
Carb.  of  Ammonia 


top.  Acetate  of  Lead  " 


Distilled  Vinegar. 
Juise  of  Lemons. 
Aqua  Fortis. 
Salt  of  Lemons. 
Oil  of  Vitriol. 
Alum. 

Plaster  of  Paris. 
Green  Copperas. 
Blue  Vitriol. 
Epsom  Salts. 
Glauber  Salts. 
White  Vitriol. 
Saltpetre. 
Lunar  Caustic. 
Prussian  Blue. 
Rochelle  Salt. 
Verdigris. 
Table  Salt. 
Goulard. 
Smelling  Salts. 
Chalk,  Marble,  &c, 
Sugar  of  Lead. 


SUBLIMATES  are  chemical  preparations,  the  basis  of 
which  is  quicksilver.  In  CORROSIVE  SUBLIMATES,  the 
quicksilver  is  extinguished  either  by  vitriol,  potter's  clay, 
or  some  other  ingredient. 

SUBLIMATION  is  a  similar  process  to  distillation;  only 
solids  (such  as  metals)  are  employed,  instead  of  liquids. 

Thus  the  fine  blue  used  by  painters  is  a  sublimate,  and 
made  thus :— Take  2  parts  of  quicksilver,  3  flower  of  brim- 
stone, 8  sal  ammoniac;  and  (having  ground  them)  put 
them  with  the  quicksilver  into  a  glass  retort,  luted  at  the 
bottom:  place  the  retort  in  a  sand-heat;  and  (when  the 
moisture  is  given  off)  you  will  have  a  splendid  blue  sub- 
limate for  painting. 

N.  B.  It  may  be  profitable  to  remind  the  pupil  that 
when  the  termination  "  ous"  is  used,  it  implies  that  the 
substance  has  less  oxygen  than  when  the  termination  "  io  " 
is  added— thus,  sulphurous  acid  contains  less  oxygen  than 
sulphuric  acid,  &c. 


INDEX, 


1 

Page 

Page 
Air  dries  linen          .       151 

not  conductors  173 

elements  of  219 

not  reflectors.     179 
radiators  182 

expanded  by  heat  102,  268 
full  of  smells  143 

ABSORPTION  of  HEAT  .  .  173 

not  conduction  173 

healthful  242 

of  light  339 

heated  202  226  270 

ACCIDENTAL  COLORS  ..   375 
Acetate  of  copper  .  ..»  454 

not  by  the  sun  181,  226 
hotter  when  the  sun 
shines  227 

Acid  of  drinks  248 

in  a  room       .      .         270 

of  fermentation  .  .  248 
Acids  dissolve  ice  32 
Activity    affected     by 
cold                   90 

inflammable,  see  hy- 
drogen. 
needful  for  fire  53 
non-conductor                19 

"    by  heat  92 

of  cities    unhealthy 

Aerated  water  247 

223  242 

Aeronauts  feel  pain  138,  229 
Age   affects    power    of 

of  the  country  heal- 
thy     223  242 

walking  392 

on  land  colder  than 

Aged  people  far-sighted 

on  water  207 

361,  363 
AIR  219  268 

on  land  cold  at  night  211 
preserved  normal        2^4 

always  in  motion  ..  270 
ascends  when  hot  .  .  268 
bad  conductor  15,  165,  217 
bad  radiator  202 

purified  by  lightning    32 
radiates  no  heat  202 
rarefied  is  noiseless.   139 
rarefied  bad  conduc- 

cold     166 

tor  of  sound    383 

colder  than  blood  .  .   169 
composed    of   two 

"        by  a  crowd..  239 
rusts  iron  .  .  .'  231 

gases      .         .  30  219 

still  before  a  temDest  139 

condensed  by  cold  .  .  269 
cooled  by  convection  202 
cooled  by  rain  150 

use  of  oxygen  in  220 
varies    in    tempera- 
ture              313 

cools  hot  iron  227 

Air-gun  101 

density  diminished  by 
rain    315 

Air-pump  freezes  water  335 
Aisles  famous  for  echoes  384 

descends  when  cold  269 
double  current  in  a 

colder  than  galleries  229 
Alcohol  !  .  .  249 

room  270 

from  sugar  ..          ,.  250 

(For  Index  to  Part  III,  see  page  485.) 


456 


INDEX. 


Page 
Alcohol,  boiling  point  of  115 
Am                107 

Pag* 
Balloons   138 

inflated       107 

bottled  248 

rise  (sec  aeronauts.)  107 
Balls  of  fire      .      .  .  .         14 

froth  of                 .  .     248 

"   increased  by  heat 
107,  248 
Alkali       50 

Balusters  wet  200 

Banisters,  see  balusters. 
Barley  malted  251 

Anemometer           •  •  •     294 

affected  by  cold  .  .  300 
frost..  299 
"         heat  ..   302 
"         thaw..  300 
"         wind..  299 
rules  for  its    rise 
and  fall  .  .  299,  308 
sudden  change  in  302 
use  of    298 

Anglers  hate  a  magpie  145 
Angle  of  incidence  ....  344 
of  reflection  344 
Anhydrous  sugar  250 
Animal  fluids  conduc- 
tors         20 

ANIMAL  HEAT  .  .  83  258 

caused  by  com- 
bustion       85 
Animal  and  vegetable 

varies  most  in  win- 
ter    306 

"  least  in  summer  306 
when  highest.  .  .  306 
"      lowest  ...  307 
Barren  land  collects  no 
dew  194 

Animals  for  bode  rain  .  .   141 
Ants  love  honey-dew  .  .  204 
Appetite,  see  hunger. 
Apples  full  of  air  104 
roasted  103 

Bass  notes  in  music  .  .  379 
Bass  preserves  flowers 
from  frost  191 

soft  104 

April  'showers                  288 

Bathing,  danger  of  359 
"     with  ether  for  in- 
flammation    ....  148 

Argand  lamps  82 

Ascent  in  balloons  pain- 
ful         138 

Beakers  broken  by  hot 

Ashes  soften  water  ....   322 
Asses  bray  in  wet  wea- 
ther                             141 

Beasts  covered  with  hair  165 
Beds  damp  ....  149 

Atmosphere  (see  air)  .  .  284 
Aurora  borealis               136 

BEER,  fermentation  of  249 
flat  255 

colored  136 

froth  increased  by 
bottling  248 

white  .  .  .            136 

a  prognostic  ..   136 
Autumn  tints  .  .  .            372 

froth  increased  by 
heat  107,  248 

Avenues       .                   353 

stale  255 

Azote,  see  nitrogen. 

Bales  catch  fire  spon- 
taneously .  .                   60 

soured  by  lightning   32 
not  old  beer  ....     32 
spoiled,  if  the  vent- 
peer  be  left  out  255 

INDEX. 


457 


Page. 
Beer,  yeast   added  to 

make  it  work 251 

(see  vent  peg*) 

Beer-vats  dangerous  . .  245 

Bells  heard  at  a  distance  380 

cracked,  sound  harsh  378 

ringing  dangerous  . .     23 

silenced  by  a  touch  378 

Bell-metal 378 

Bellows 55 

Bible  explained..   164,  195 
311 

Birds  covered  with  fea- 
thers..,    165 

Bins   purified  by  lime,  259 

BLACK 371 

cloth  warm 174 

eyes 179 

glass  for  spectacles  376 
hat  turns  red  at  the 

sea-side 321 

hole  of  Calcutta  . .   240 

Black  kid  gloves 176 

lead 232 

prevents  rust  . .   232 

mist 137 

skin 178 

tea-pot 184 

used  by  cotters  184 
set  on  a  hob  to 

draw 184 

will  never  blister '. .   178 
Blacksmiths  strike  fire 

by  nails 95 

Bladders    inflated    by 

heat 102,  269 

BLAZE,  blue 50 

green 50 

yellow 50 

between  the  bars 

of  a  grate.. ..     50 
Blazing    coals    burn 

quickly 44 

Blood 222,  238 

purple 222 


Blood,  red 222, 

Blowers 

Blowing  cools  broth,  tea 

&c 168, 

Blue 

sky 

spectacles 

sublimate 

Body,  fuel  of 

warm 84, 

Boiler,  see  saucepan. 

BOILING 

"     WATER  bubbles . . 

furrof 

makes  it  flat  . . 
is  in  a  ferment 

kept  hot 

rattles 

runs  over 

swells 

one  pot  will  not  boil 

in  another 

retarded  by  a  spoon 
"     by  salt,  sugar 
without  touching 

the  boiler 

Boiling  point 

Boots  hot  when  dusty 

Bottled  ale,  &c. 

Brackish  water  unfit  for 
railway  engines  .... 

Bracing  weather 

Bread  heavy 

made  with  yeast 

Breath  exhaled 

inhaled 

visible  in  winter 
Breathing  described  . . 
difficult  on  a  moun- 
tain   

previous  to  a  storm 
BREEZE    at    watering 


evening . 
land  ... 


Page 
223 
70 

293 
454 
126 
375 
454 
86 
258 

213 
111 
236 
257 
214 
187 
112 
111 
110 

113 
113 
114 

114 
115 
181 

248 

237 
140 
258 
257 
223 
221 
200 
224 

229 
229 

291 
290 
291 


20 


458 


INDEX. 


Page 

Breeze,  morning 289 

of  islands 291 

sea 290,  291 

speed  of 293 

(see  wind.) 
Bricks  for  cold  feet  ...  162 

Brick  stoves 163 

Bricklayers  cannot  work 

in  a  frost 334 

cover  work  with 

straw 334 

Bright  day  exhilarating  137 

Brilliancy 339 

Brine  retards  boiling. .  114 

tested 335 

Britain  cloudy 123 

Broth  cooled  by  breath  227 
by  convection  228 
by  stirring  . .  228 

Bubbles  in  tea 387 

of  boiling  water  111 

Bulk  for  bulk 107 

Burns  cured.. 148 

Buint  stick  twisted  ..  374 
Burning  glasses 10 

Calcutta,  black  hole  of  240 

Calcareous 225 

Caloric 9 

Cambric  handkerchiefs 

cool 172 

Camphor  antiseptic  . . .  389 

CANDLES 74 

burn 74 

cotton,  not  easily 

blown  out 78 

easily  blown  out  65,  77 

extinguished 79 

by  a  pin 81 

breath 77 

paper 79 

flame  blown  out  . .     55 

hot  76 

hollow  76 

pointed 77 


Page 

Candle-flame  purple  be- 
low       76 

tends  upwards    77 

yellow 76 

Candles,  gas  of 84,  262 

held  at  a  door  270,  271 
hottest  above  the 

flame 78 

give  light 75 

make  glass  damp    78 

need  snuffing 80 

Palmer's 80 

prevent  our  seeing 

abroad 352 

reflected  in  a  win- 
dow    352 

rekindle  quickly . .  55 
rush,  easily  go  out  78 
shadow  cast  by  . .  352 

smoke  of 81 

.  spirt 146 

suddenly  introduced 

give  pain 339 

wax,  need  no  snuf- 
fing       80 

Candlestick  rags  catch 
fire  spontaneously..     61 

Cannon  balls  hot 101 

boring 100 

Canvass  flower-awning  191 

Capillary  attraction  75,172 

388 

vessels 83 

Captain  Ross 381 

Capuchin 317 

Carbon 40,  74 

in  the  blood ....  238 

Carbonate  of  ammonia  454 

of  lime  ....   454 

CARBONIC  ACID  GAS  43,  238 

absorbed  by  leaves  225 

accumulation  of, 

prevented 246 

deleterious 238 

detected 239 


INDEX. 


459 


Page 

Carbonic  acid  gas  dis- 
sipated by  red  heat  246 
in  human  bodies . .     84 

ofthesoil 225 

sources  of 245 

CARBURETTED  HYDROGEN 

GAS 263 

Carpenters' tools  hot..     99 

Carpets  warm 157 

Carriage  in  a  storm  . .  26 
wheels  catch  fire  98 
windows  misty .  197 

Casks  charred 72 

Cart-grease 98 

Cathedral  aisles  famous 

for  echoes 384 

CATS  in  wet  weather  . .   140 
prowl  by  night  . . .  342 

rub  their  ears 142 

see  in  the  dark  . . .  341 
wink  before  a  fire  342 
Cattle  low  in  wet  wea- 
ther    140 

in  a  storm 25 

Caustic  lime 390 

lunar 454 

Caverns  famed  for  ech- 
oes    383 

Ceilings  sooty 71 

Cellars  cold  in  summer  231 
warm  in  winter  231 

Cerebellum 391 

Cerebrum 391 

Chalk    454 

Champagne  acid 248 

CHARCOAL 72 

bad  conductor 156 

fire  very  hot 72 

"  deleterious 245 

purifies  water 72 

removes  taint 72 

Charring  bread 73 

casks 72 

wood 73 


Page 

CHEMICAL  ACTION 3(i 

Chestnuts  crack  when 

roasted 102 

not  if  slit 103 

Chimney  pots 70 

flues  long 64 

'•'  short 64 

raised  above  a 
house  ...  64,  68 

CHIMNEYS  SMOKE 63 

if  a  room  be  too 

close 63 

remedy 64 

in  old  farm  houses  69 

valleys  ,, .     67 

in  wind 70.  108 

if  too  long..  64|  108 
Chimneys  smoke  if  too 

short 64 

remedy 66 

large 69 

remedy 70 

when  the  draught 

is  slack 65,  69 

when  the  door  is  on 
the  same  side  . .     68 

remedy 68 

when  they  need  re- 
pairing       69 

sweeping 69 

when  two  fires  are 
in  one  room ....     67 

remedy 67 

China  broken  by  hot 

water 120 

Chlorophyll 372 

Choke  damp 244,  261 

Church  bells  heard  at  a 

distance    139,  380 
congregation  drowsy  241 
Churchyards  smell  offen- 
sively    265 

Chyle 221 

Chyme 221 


460' 


INDEX. 


Page 
Cinders    iron                     48 

Clouds    distance  from 

lighter  than  coals     48 

the  earth  123 

soon  heated  48 
will  not  blaze....     52 

edges   most    lumi- 
nous     369 

Cirro-cumulus    clouds    130 

electrical  .  .  .            1^5 

Cirro-stratus  clouds  .  .  .   130 
Cirrus  clouds    .               128 

fall   in   rainy  wea- 
ther    ..                 315 

Citizens  pale    222 

fantastic    .    ...         131 

float.  1*?3 

City  air  unhealthy  242 
Clay  for  furnaces    .       163 

gather  round  hills  132 
height  of    T'   1->4 

Clean  kettles   174 

Cleanliness  connected 
with  the  dietary    93 

highest  in  a  fine  day  115 
increased  by  wind  166 
intermediate  ....     130 

Clear  day  overcast          285 

lio-ht      115 

fire  burns  slowly       44 

lowest  124 

nights     exhilarat- 

morning red  1  27 

ing                         137 

motion  of  .  .            1^7 

Clocks  heard  at  a  dis- 

nimbus     131 

tance     380 

rain  indicated  bv      131 

Close  rooms  unhealthy  240 

red  1  26  369 

Cloth  collects  but  little 
dew       143 

round     mountain- 
tops  182 

Clothes  slather  damp  in 

simple   ...    ....       1^8 

summer                 195 

size  of  1*^4 

wet      .      .  .  ..,    .  .     148 

s    stratus  129 

Clothing  for  workmen  154 
loose  warmest          165 

sun-set  133 
thickness  of  1  24 

promotes  warmth    164 
want  of  makes  dirt 

how  ascertained  124 
thunder  15 

agreeable  .  .   .         93 

vary  in  shape  ....   1  "?4 

Cloudiest  countries         1^3 

in  color      .            1^7 

where  most  abund- 

absorbed bv  wind  125 

ant                    .     1  23 

cause  of  122 

where  least  123 

cirro-cumulus           130 

use  of  1  32 

cirro-stratus  ....     1  30 

velocity  of  294 

classes  of  128 
color  of  124,  126 
compound  ....         130 

wind  affects  them 
123,  125 
yellow  133,  134 

cumulo-stratus         131 

cumulus            .   .     129 

Cloudy  night  warm  ...   189 

differ  from  fog  122,  209 
dissinated  .  .  .   125.  133 

.     oppressive  ...   137 
Coale:as..               .  74,262 

INDEX. 


Page 
Coal  mines  explode . . .  262 

Coals  black 371 

blazing 44 

frotesque  figures  of   46 
>r  fuel . . . . 48 

smoke 45 

Coffee,        spontaneous 

combustion  of 61 

Coke 59 

for  fuel 48 

spontaneous   com- 
bustion of 60 

COLD  WEATHER   affects 
the      barometer 

299,  306 
makes  us  love  fafc    89 

activity 90 

out  of  doors 293 

promotes  hunger  .     90 
Colder  some  things  than 

others 155 

Colds  from  wet  clothes  149 

Collapsing ... 104,  269 

Color  of  clouds 123 

electricity  ...     35 

Colors 364 

accidental 375 

dark,  warm  ....   175 

light,  cold 175 

vary 370 

Combining  not  mixing     31 
COMBUSTION  (see fire)..     83 

animal 84 

cause  of 43 

chemistry  of ...  40,  43 
from  fermentation     60 

elements  of 43 

heat  of 40 

increased  by  wind      55 

in  the  veins 84 

produces  light 51 

spontaneous  . .'.  60,  81 
COMMUNICATION  OF  HE\T 

155 
Compound  clouds  130 


Page 

COMPRESSION   100 

differs    from    con- 
densation       99 

CONDENSATION 99 

Condensed  air 269 

CONDUCTION  55 

not  absorption..   173 

CONDUCTORS,  best 56 

worst 56 

animal  fluids ...  20 
not  absorbers  . .  1 73 
of  lightning ....  27 

dangerous 29 

CONVECTION 202.  213 

Convective  currents  226. 270 

cool  broth 228 

iron 227 

Cooking    vessels    with 

wooden  handles 156 

Cooper     applies     hot 

hoops 117 

Copper  for  conductors      28 

sonorous   378 

tarnishes   233 

Cork  driven  out  by  heat  106 

Cornea 360 

Corns  ache  in  wet  wea- 
ther    230 

Corpse  cold 94 

Corrosive  sublimates..  396 
Cotton  bales  catch  fire  60 
spontaneously.  60 
candles  hard  to 

bio  v  out   78 

handkerchiefs  hot    172 
oiled  transparent  .  373 
Countries  most  cloudy    123 
least  cloudy  123 
Country  air  salubrious 

223,  242 
Countrymen          enjoy 

health 242 

ruddy 222 

Cowls 67,  108 


462 


INDEX. 


Crowds  dangerous  in  a 

Page 
Dark  colors  warm  ....   175 
radiate  heat       183 

produce  drowsiness  242 

Davy  Sir  H   263 

head-ache  .  239 
vitiate  air  239 

Day  -  light      produces 
hunger  .   .       88 

unhealthy  240 

mitigates  cold    88 

Crucibles  made  of  pla- 
tinum    236 

Dead  bodies  cold  94 
smell  266 

Culinary  vessels  186 

taller  than  livino-  390 

have  wooden  handles  156 

Deafness  382 

should  be  sooty  ....   186 

Decanting  liquor    ....  256 

Cultivation     promotes 
dew  194 

spirting..  266 
Decomposition  .  .  .          246 

warmth  ...  152 
Cumulo-stratus  clouds    131 

Deep     water     freezes 
slowly  331 

Cumulus  clouds  129 

Depression  of  spirits  .  .   137 

Cup  in  a  pie  116 

Descent  in  a  diving  bell 

use  of  117 

painful  138 

why  full  of  juice  117 
Currents  of  air  270 

Deserts  hot  and  dazzling  374 
Detonating  powder  .  .  .   101 

DEW  188 

Damp  balusters  200 

cause  of  209 

beds    ...      .         149 

deleterious  203 

clothes  195 

differs  from  rain  .  .  209 

house  200 

distilled  after  a  hot 

Dandelion      forebodes 

dav  202 

rain  142 

especially    if    the 

DANGER  IN  A  STORM  ...     18 
in  attics  and  cellars    22 
a  crowd     25 

wind  be  westerly  202 
in  fine  nights  only    189 
distilled  unequally  192 

in  a  theatre,  &c...     25 
before  a  fire  25 

in  open  places  190 
in  valleys  and  hollows  191 

near  a  tree                  19 

in  a  river      19 

cultivated  lands  .  .   194 

flocks  and  herds  are 

grass  194 

exposed  to   ....     25 

hair  201 

those      who      bar 

hat    201 

shutters    .  .            24 

leaves  &c  193 

those    who    drive 
fast  21 

none  beneath  a  tree.  190 
a  flower  awning  191 

lean  against  a 
wall  23 
or  carriage.     26 
who  ring  bells  19,  23 
run  ..           .21 

a  hedge  or  wall  191 
none  in  a  cloudy  night  189 
in  a  windy  night  191 
especially       if 
easterly  ....  201 

INDEX. 


463 


Page 
Dew,  none    on  stones,  191 
cloth,  deserts.  grav- 
el metal    rocks 

Page 
Dry  wood  burns  best  .  .   106 
snaps  about..   106 
Driest  months  307 

'wool    '            '  194 

Dew-drops  round  205 
flattened  205 

Duck  dry  in  water  ....   206 
noisy  before  rain  141 

roll  on.  cabbasres  205 

Dullness  339,371 

K       roses         206 

Dunghills  hot  258 

Digestion         ....    .  .       90 

Dinner  covers    ...  ....   187 

Dirt  warm                          93 

Ear  trumpets  382 

Distant  bells  heard  380 
clocks     .       .  .           381 

EARTH,  bad  conductor.  170 
cool  in  summer.  .  .   170 

objects  appear  small  354 
sight  361  363 

cools  after  sun-set    189 
in  a  fine  night  189 

spectacles   for  362 
Distance  makes  things 

cracks  by  frost  ...  332 
crumbles  in  spring  333 
warm  in  winter.  .  .   170 

warmer    than    air 

Divers  suffer  pain    138  230 

by  day  189 

Diving  bell                       138 

Earth-fog  204 

Doors  swell  and  shrink  143 
Dogs    uneasy    in    wet 
weather  140 

Earthen  tea-pots  184 
set  on  a  hob  to  draw  184 
Eat  more  in  cold  wea- 

Dou2"h fermented            257 

ther  90 

set  before  a  fire  to  rise  258  - 
Double  concave  glasses  361 

less  in  warm  wea- 
ther       90 

convex  fflasses          362 

Echo  ....  383 

Down  warm  165 

Echoes,  two  or  more  .  .  385 

Draining  lands  promote 

remarkable  .  .  385 
EFFECTS  OF  HEAT  101 

DRAUGHT  at  a  door  ....  294 

EFFERVESCENCE  247 

key-hole.  294 
window  .  .  294 
slack  65  23 

soon  subsides  257 
Effervescing  draughts.  247 
Egg,  component  parts  of  254 

Dreams  390 

discolors  silver  spoons  254 

Driving    in    a    storm 

new-laid   cold  167 

stale    warm  167 

Drops  of  rain  roll  on 
dust  206 

"  smells  offensively  254 
tests  brine  335 

Drowned  men  restored     99 

tested  167 

Drowsiness  at  church  .  .  242 
Drums  379 

Egypt  not  cloudy  123 
ELECTRICITY  affects  the 

Dry  toast  for  invalids.     73 
wood  for  kindling     49 

clouds  ....  125,  127 
excited  by  friction    34 

4G4 


INDEX. 


Electricity  felt  at  the 
elbow  joints  34 
hot  84 

Page 
Eyes  affected  by  sud- 
den light  ".  339 
affected  by  the  sun  375 

black  179 

of  clouds  11,  127 

cornea  of  360 

positive  and  nega- 

retina of  360 

tive  22 

two  use  of  343 

resinous  and  vitre- 
ous    11  23 

"    see  single.  .  ..   343 

source  of  heat  ....     11 
Electric  telegraph  ....     36 

Face  soon  scorched  ...   182 
Fanning  167    293 

Elements  of  air  40 

Far  sight   361    363 

of  fuel  40 

spectacles  for  .  .   362 

Emetic  tartar  45  i 

Farm-houses  smoke  .  .     69 

Epsom  salts   .  .        ....   454 

Fat  men  swim  best  .   .  337 

Esquimaux  love  blubber   91 
Equatorial  current.  .  .  .   278 
ETHPR   51 

Fat  pleasant  in  winter    89 
not  in  summer    91 
Feathers  warm  165 

boilin0"  point  of    .   115 

Feelin°-  392 

used  for  freezing  .  .  335 
"    inflammation, 
scalds  burns,   148 

Feet  cold  before  a  fire.     57 
wet  dangerous  ....   148 

differs  from  pu- 

European skin  white  .  .   178 

EVAPORATION    147 

trefaction  252 
of  dough  257 

freezes  ....   335 
of  sea             276 

produces     corn- 

EVENING  CLOUDS.  .  .126,  133 
grey  135 

requires  water.  .   155 
Fender    and    fire-irons 

red  126  133  370 

cold  173 

yellow  .  133,  234 
Evergreens  frost-bitten  212 
Ewers  broken  by  frost.  325 
EXPANSION  by  HEAT  101,  117 
Explosion    of    roasted 
chestnuts      .  .   102 

Fiddle-strings   musical  378 
snap  from  wet  316 
Fine  weather  braces  .  .   140 
indications  of  134 
Finger  feels  cold  when 
wet  148 

of  gunpowder        103 

FlRF         39 

of  mines  263 

air  needful  for  ....     63 

Extinguishers  79 

bellows  use  of  ...     55 

made  of  paper    79 
Eves  adapt  themselves 

black  and  red  ....     44 

to  light  340 

not  in  frost  62 

affected    by    blue 

fflasses                   375 

affected  bv  fire-lip-ht  374 

charcoal  ..                  72 

INDEX. 


465 


Page 
Fire,  charcoal  danger- 
ous      245 

Pag« 

Fishes  ascend  and  dive  338 
seem  nearer  than 

clear                  .  .  44   53 

they  are  ....       359 

damp              ..         261 

cold   93 

differs  from  animal 
heat     85 

FLAME  of  a  CANDLE  ...     75 
described  »  »     76 

dull,  cause  of  65 
effect     uponv  "  the 

blown  out  easily.  .     77 

eyes    341    374 

extinguished    •  .  •       57 

hot  75 

by  water  57    106 
fiercest  in  winter       53 

hottest  above  ....     78 

out  of  doors  .       54 

pointed  77 

gas    generated  by    84 
grotesque     figures 

purple  and  yellow    76 

in                ....     46 

Flame  of  a  fire  between 

heat  of     258 

the  bars  of  a  grate  50 

how  increased  53  63 

blue   50 

hot     44 

kindled  at  the  bot- 

Flame yellow  5O1 

tom    47 

Flannel  warm    93- 

lighted  with  paper 
i       and  wood  46 

used  for  foot-  warm- 
ers                          93  ' 

li^ht  dazzles  ....     340 

Flash  sec  li,cf'fitfi'irticr 

light  variable  ....     52 

Flat  beer  &c  256 

luminous  50 

melts  metal    ...    .   121 

Flavor  discerned  by  the 

mottled  .       45 

taste    .  392 

out  of  doors   45 
poker  draws  up  .  .     56 

Flax    burns  spontane- 

radiates  heat   ....   182 

Flint  and  steel  strike 

red  hot  44    330 

fire    96 

reflected    on    win- 
dows     352 

Flocks    dangerous    in 
storms      .  .           ...     26 

spotted  .  ,  45 

FLOWING  WATFR  freezes 

sun  dulls  it  53 

slowly   329 

thaw  dulls  it  55 

makes  rough  ice  .  .  330 

wind  intenses  it    .     55 

oscillates  324- 

See  combustion. 

pure  324 

Pire-irons  cold  161,  174 
hot  174 

Flower  awnings  arrest 
dew  190 

rust  ...     231 

purifv  air         .  .  232 

*'    most  in  win- 
ter    232 

Flowers  sme!l  sweetest 
at     night     and 

"    prevented  .  232 
2 

before  ram  144 

0* 

466 


INDEX. 


Page 
Flowers  forebode  rain    142 

Flues  64 

blacked  183 

long,      good      for 

draught 66 

short,  bad        "         65 
See  chimney. 

Flutes 379 

Fly  poison 390 

Foam,  white 371 

FOGS 208 

arrest  sound 381 

cause  of 123 

differ  from    cloud 

122,  209 

mist 209 

dispersed  by  wind  210 
dispersed   by   sun  209 

frozen 212 

in  autumn 209 

";iacrease  distance  .  141 

in  marshes 208 

in  valleys 210 

magnify 141 

none  m  a  frosty  night  209 
I  Food  concerted  to  blood  221 
cooled     by    the 

breath 293 

!  Food,  want  of,  produces 

hunger 89 

want  of,  produces 

laziness 89 

aversion  to  clean- 
liness       93 

"  to  ventilation     93 
Foot-prints  frozen ....  325 

Foot  warmers 162 

Forked  lightning 12 

,  Forests  catch  fire  spon- 
taneously       99 

cold 152 

France  warmer  than  of 

yore 153 

FREEZING  MIXTURES.  ..  335 
FRICTION  {see  riibbing)    97 


Pag* 

Friction  excites  electri- 
city   34 

sets  forests  on  fire    99 

Frogs  cold 94 

croak  before   rain  141 

FROST  affects  barome- 
ter..,,   299 

"     sound  . .  380 

braces ,.   140 

breaks  ewers 325 

"  tiles,  stones,  rock  325 

"  pipes.. \. 327 

cracks  earth 332 

"     mortar 333 

expands  water 325 

on  windows  ......  220 

prevents  fog 209 

stops  work.. * 334 

warmer  than  thaw  332 

Froth  of  beer....  107,  248 
of  fermentation  . .  255 
white 372 

Frozen  water  warm  . .  330 
ruts  and  foot-prints  326 

Fruits  cool  the  blood . .  92 
fall  to  the  earth  . .  388 
pleasant  in  summer  91 

Fuel,  dry  burns  well  ,  „     49 

elements  of 40 

for  the  body 86 

wet  burns  badly . ,     49 

Fulgurites 35 

Fumigation     for    sick 

rooms 389 

Funnel  (see  flues} 64 

FUR,  bad  conductor  . .   156 

for  clothing 164 

warm 165 

Furnaces  of  brick  ....   163 
lined  with  clay  163 

Furr  of  kettles 236 

steam-engines  dan- 
gerous    237 

Gallery  hot 229,296 


INDEX. 


46T 


Page 
(jas     74  109    19 

195  225  283.  289.  328.  ^ 

differs  from  liquid  220 
elastic    220 

Gold  never  tarnishes  .  .  235 
Goodness  (see  wisdom). 

invisible                     ^19 

jet  of  79 

Grape  juice   needs    no 

of  candles                  ^63 

veast  254 

Gau/e   wire   of  safety- 

ferments  249 

lamps  264 

makes  alcohol  250 

prevents  explosion  264 
Geese  noisy  before  rain  141 
German  silver  tarnishes  235 
tinder                   100 

"     carbonic  acid  250 
Grapes  never  ferment  .  254 
Grass  promotes  cold  .  .   152 

Germany  war  me?'  than 
of  yore        .          .  .       153 

Grate  (see  stoves). 
Gravel  collects  no  dew  194 

Germination                     288 

Gravity  387 

Ghosts  266 

Gray  morning,  sign  of  a 

fine  dav  134 

Ginger-pop    248 

evening,  sign  of  wet  135 

acid  248 
GLASSFS  broken  by  hot 

GREASE  liked    in  cold 
weather  89 

water  119 

loathed  in  hot  ....     91 

broken  if  set  on  a 
hob      .              120 

prevents  rust  ....  145 
used  for  wheels  .  .     98 

covered  with  mist  198 

Green  color  372 

"  if  brought  from 
cellar  199 

wood  does  not  burn  105 
"  does  not  snap 

dulled    by    a    hot 
hand  198 

when    burned  205 
Grottoes     famous     for 

"   by  breath  &c  199 

echoes      383 

mist  of  soon  sub- 

Ground  frost  209 

sides  198 

Growth    promoted    by 

moonlight  203 

Guinea  fowls  squall  be- 

soon  cools          196  198 

ground  not  trans- 

Gulls fly  to  sea  145 

parent                   373 

to  land     .  .    .   145 

S?:e  looking-glass. 
Glauber  salts  454 

Gunpowder  explodes..  103 
Gusty  weather  makes  a 

Gloves    black  kid           176 

smoky  house  ...   .       70 

Lisle  thread.  .  .   176 
Glow-worms  glisten  by 

HAIL  312 

night  342 

accompanied  with 

Gluten  251 

thunder  313 

ferments                252 

Hail  cause  of  313 

GOD'S  WISDOM  153,  166;  193 

falls  in  summer  .  .  313 

468  INDEX. 


Page 

Hair,  bad  conductor  . .  156 
covered  with  dew  201 

warm 165 

Halls  famous  for  echoes  384 
Halo  round  the   moon  136 

Handles,  wooden 156 

metal 156 

Hard    work    promotes 

hunger  .*. 87 

water  bad  for  wash- 
ing    234 

Hartshorn 253 

Hat  covered  with  dew  200 
turned  red  at  the 

sea-side 320 

Hawks  see  near  and  far  363 
Hay-stacks    catch   fire 

spontaneously 61 

Haze  round  the  sun. . .  136 
"     the  inoon  136 

affects  sound 381 

Head  aches  in  a  crowd  239 

itches  in  wet  weather  142 

Hearth-rug  warm  ....   159 

Hearth-stone  cold 159 

hot 160 

HEAT 9 

absorbed 37 

and  light 51 

affects  barometer .  302 

"     sound 380 

animal  ...  83;  223,  258 
applied  to  the  bot- 
tom of  boilers  ..214 
communication  of  155 
conduction  of  ....  155 
effects  of  ...  10  to  101 

evolved 37 

"     by  compres- 

'  sion 100 

expands  air 102 

expands  water ....   334 
from  beaten  iron  .     94 
increased  by  accu- 
mulation       60 


Page 

HEAT,  LATENT 38,  95 

of  candles 75 

dunghills 258 

fire 258 

ice 38 

human  bodies  84,  258 

lime 265 

radiates ...   182 

reflection  of 179 

sensation  of 9 

sources  of  . .   10  to  101 
Heating  rooms  by  stoves 

103,  183 

by  steam 183 

Heavy  bread 258 

Hemp,  spontaneous  com- 
bustion of 60 

Herds     dangerous    in 

storms —     25 

Hedges  increase  warmth  152 

Hills  larger  in  a  fog. . .   141 

seem  more  distant  141 

HOAR  FROST 211 

not  found  on  trees  212 
under  shrubs,  &c.  212 

of  frozen  fog 212 

on  clear  nights  only  211 

"  grass 211 

"  tombstones 177 

very  partial 211 

HONEY-DEW 203 

Honey-de  v,  ants  fond  of  204 

*  effects  of 203 

injures  plants  . .  203 
Hoops  iised  red-hot ...  117 
Horizontal  sun  and 

moon 350 

Horses  strike  fire 97 

snuff  up  air  ....  144 
uneasy    in    dull 

weather 141 

Hot,  cloudy  night  op- 
pressive     137 

I  Hot  water 187 

melts  sugar  ....  323 


I 


INDEX. 


469 


Hot  weather  abates  ac- 
tivity   

abates  appetite, 
produces  love  of 

fruit 

"   dislike      of 
grease . .  . 

Hottest  place  at  church 
229, 

Houses  catch  fire  spon- 
taneously .... 
gather  damp  . . .  200 
seem  more   dis- 
tant in  a  fog 

smoke  in  valleys    67 
Hull  of  ships  seen  last  358 

Hunger 87  t< 

promoted  by  cold 

"  day-light 

"  rapid  digestion  . 
"  singing,     speak- 
ing, work .... 
See  appetite. 

Hydrogen  gas 40,  74 

of  fuel 220 

ICE 

contains  heat 38 

dissolved  by  acids  332 
friction  99 
salt  . . .  332 
sun  .  . .  121 

grows  thicker 329 

lighter  than  water  325 
Ice -bergs    famous  for 

echoes 384 

IGNIS  FATUUS  ....  266,  267 

cause  of 266 

Impure  water  purified  72 
Indian  mode  of  striking 

fire 

Inflammable  air, 40,  74 

Insects  in  wet  weather  145 
Insensible  perspiration  197 
Intermediate  clouds . . .  130 


Page 
92 

Page 
IRON  affected  by  light- 
ning       36 

91 

cinders              •  •    «     48 

cold     159 

91 
91 
296 
59 

contains  latent  heat    95 
cooled  by  air  227 
"        convection  227 
"        radiation  .   227 
good  conductor  ...  173 
heated  by  blows  .  .     94 
rust  231 

200 

"  when  most  com- 
mon    231 

141 

"  prevented     .    .     232 

67 

"  scales     231 

858 

)  91 

90 

Ironin01  box     •      147 

.  88 
90 

Islands  equable  in  tem- 
perature                291 

88 

subject  to  wind  .  .  .   290 

,74 
220 

Itching  in  wet  weather  142 

Jack  o'-lantern  (see  ig- 
nis fatuus)  266 

3^5 

Java  (WP  jungles)  ....     241 

38 
3?>? 

Jet  of   flame  through 
bars  50 

99 
83? 

Judges  vi.  illustrated  .  195 

121 

39q 

Jungles   of  Hindostan 
fatal  241 

325 

384 
267 
266 

72 

97 
>,  74 
145 

KETTLE  boils  over  111 
quickly  if  cover- 
ed with  soot  .   174 
slowly  if  clean  .  .  174 
"      if  new.  ..   174 
bottom     should 
be  sooty  185 
cold  when  water 
boils  186 

197 

furr  of  236 

130 

holder..            .  157 

470 


INDEX. 


Page 
Kettle-lid  clean  1  85 

T            .                            Pa?e 
Leaves  in  a  pond             '5S7 

hot    .  .         .   186 

light  green  in  spring  372 
pale  in  dark  places  372 
promote  cold  152 
yellow  in  autumn  372 
Lemons,  juice  of.  .  .  .       454 

Kettle    not    full    after 
boiling  Ill 

runs  over    .  .           Ill 

through  the  spout  112 
sin°-s  109 

salt  of                454 

steam  of  216 

Lid  of  kettle  bright...  185 
hot  186 
rattles...   112 
Light  bread  257 

top  bright   185 

Kilkarney,  echo  of  386 
Kindlin0"  fires    46 

colors  cool                175 

dry  49 

LIGHT  51    338 

wet  48 

absorbed  339 

Ladies  fan  289 

composed  of  vari- 
ous  colors    364,  370 
divided  by  a  prism  364 
from  a  flint  96 

Lakes      which      never 
freeze  331 

Lamps  74 

compression  ....     100 

Argand  82 

of  candles  76 

smoke                     82 

fire     50  5'> 

spirt  149 

houses,  trees,  &c.  338 
the  sun  '.  338 

See  candle. 
Lamp-glasses  82 
Land  air  cold    .  .     .  .     207 

reflected    ....           339 

speed  of  337,  338 
sudden,  painful..  .   339 
Lighting  fires  46 

Land  breeze  unhealthy  290 
cools  faster  than 
water  »                207 

LIGHTNING  11 

Laplanders  clad  in  skin  171 
Larvae                               146 

affects  iron  &  steel    35 
'    electric  tele- 
graph ....       36 

LATENT  HKAT  38,  95 
Laundress    147 

balls  13 

Laziness  caused  by  want 
of  food  ..     89 
by  heat  ....     92 
Lead,  dullness  of  234 

barks  &  snaps  trees    34 
clouds  12 

comes  from  clouds    22 
"       from  earth.     22 
conductors  28 

tarnish  of  .  .          234 

Leanness  from  starva- 
tion       86 

dangerous   29 

followed  by  rain  .  .     17 
by  wind  ...  17 
follows  dry  weather, 
not  wet  33 

LEAVES  absorb  carbonic 
acid  225 

collect    dew    une- 
quallv     192 

forked  12 

exhale  oxygen  .  .  .  224 
green  .                  .  372 

fuses  metal  32 

kills  animals  .  .          14 

INDEX.  471 


Page 

Lightning  knocks  down 
houses,    churches, 

&c 29 

magnetic 36 

maims 14 

odor  of 35 

passes  down  the  out- 
side of  a  tree  . .     20 
passes  through  the 

inside  of  animals    20 
produces  fulgurites    35 

purifies  air 33 

rare  in  winter 33 

returning  stroke . .     23 
scorches  trees ....     34 

sheet 13 

speed  of 18 

straight  13 

summer 17 

common  in  . .  33 
turns  beer  sour  . .  32 
milk  sour ....  30 
not  old  beer..  32 
not  porter  ...  32 

two  flashes 13 

See  danger ,  safety. 

Lilac  steel  rusts 233 

prevented  233 
LIME  and  water...   31,  37 

burned 260 

hot 260 

purifies  bins    259,  389 

"       sewers  259,  389 

quick  or  caustic  . .  260 

Lime-wash    for  rooms  389 

Line  of  incidence 344 

of  reflection 344 

Linen  cool  wear 171 

dried 151,295 

Linseed     oil,     boiling 

point  of 115 

LIQ.UEFACTION  . . , 121 

LIQUIDS   109 

bad  conductors.  213 
cooled  215 


Page 

Liquids  heated 214 

not  elastic 220 

Lisle  thread  gloves  ...   176 

LONDON  FOG 208 

Long  flues 107 

grass  promotes  cold  152 
Logs,  two  burn  better 

than  one 49 

See  wood. 

Looking-glass 343 

a  reflector 343 

reflects  our  image 

approaching,  &c.  345 
reflects  our  whole 

person 345 

Lucifer  matches 265 

Lunar  caustic 454 

Lungs  described 224 

Mackarel  scales,  &c.  . .   130 
Mackintosh      prevents 

cold 149 

Madness    from  starva- 
tion       86 

Magnetic  effects  of  light- 
ning        36 

Magpies  indicate   wea- 
ther   145 

Malt „ 252 

Malting 251 

Man  a  swimmer 337 

fat,  swims  best  . . .   337 
no  bigger  than   a 

crow 355 

Marble 454 

MARCH  comes  in  like  a 

lion 287 

goes  out  like  a 

lamb 287 

dry    good,    wet 

bad 288 

flowers  undesira- 
ble   288 

use  of 287 

wind  dry 287 


472 


INDEX. 


Mares'  tails 131 

Marsh  gas 261 

Marsupium 363 

Mast  of  ships  seen  first  358 

May  flowers 288 

MEAT  covers 188 

Meat  liked  in  cold  wea- 
ther      90 

loathed  in  hot 91 

roasted  by  reflect- 
ors     180 

taint  removed 389 

tainted   by  moon- 
light   203 

MECHANICAL  ACTION.  . .     94 

Mercury  of  barometer.  297 

boiling  point  of.   115 

bright 235 

concave 304 

convex 304 

Its  rise  &  fall,  303  to  308 

rises  Bom  heat.  . .   119 

METAL  collects  no  dew  193 

•    conductors 156 

feels    colder    than 

wood 158 

hotter  than  wool  157 

fused  by  tire 121 

by  lightning    32 
good  conductor. . .   156 

handles  burn 156 

reflectors 180 

tea-pots ,  184 

Milk  long  in  cooling  . .  216 
soured  by  lightning    30 

Mineral  springs 320 

Miners'  danger 264 

prevented  239 

Mirror 343 

MIST  arrests  sound  . . .    381 

black 137 

cause  of 204,  206 

differs  from  cloud  122 
dew  .  204 
fog..  209 


Paje 
Mist  increases  distance.  141 

magnifies 141 

on  windows 196 

seems  to  rise 205 

vanishes  at  sunrise 

205,  209 

white 137 

Mixing  not  combining    30 
Money  hot  in  a  pocket  15cS 

Monsoon 280,  282 

Months,  driest 307 

wettest 307 

MOON,  distance  and  size  356 
largest  at  horizon .  350 
reflected  in  water.  349 

seems  flat 356 

larger  than  stars  356 
Moonlight  makes  plants 

grow 203 

taints  meat  . .  203 

MORNING  breeze 290 

gray  . . .' 134 

rainbow 135 

red....  127,  134,  369 

streaks 127 

MORTAR 260 

adhesive 260 

crumbles 333 

hardens 260 

Motes  in  a  sunbeam  . .  228 
Mould  hardened  by  sun  153 

Mountains  cloudy 132 

cold 181 

collect  rain 316 

famous  for  echoes  384 
impede  respiration  229 

noiseless 383 

Muriate  of  soda 454 

Murky  nights   oppres- 
sive   1^7 

Musical  instruments  . .  379 
flat..  380 

glasses 379 

notes.... 379 

sounds 377 


INDEX.  473 


Myrrh  antiseptic 389 

Nails  for  matches 95 

Naves  fitted  on  hot  ...   118 

Near-sight 360,  363 

spectacles  for  360 
Negative  electricity ...  22 
Negroes,  why  black. . .  178 
with  black  eyes  179 
New  kettles  boil  slowly  174 
Night  allays  hunger  . .  88 

exhilarating 137 

oppressive 137 

produces  cold 88 

rainbow  at 135 

warm,  when  cloudy  189 

Nimbus  clouds 131 

Nitrate  of  silver 454 

Nitric  acid 30,  33,  454 

Nitrogen  42 

expired  ....224,  239 

of  air 221 

Nitrogenized 254 

Non- transparency 373 

North  wind  cold 284 

dry  284 

North-west    wind    dry  286 
299 

Northern  lights 135 

Notes,  bass 379 

flat 380 

sharp 380 

treble 379 

November  rainy 289 

Odor  of  electricity 35 

Oil,  elements  of 74 

linseed,  boiling  point 

of 115 

of  turpentine  ....   115 

of  vitriol 454 

Oiled  paper  transparent  373 
Old  people  far-sighted  361 
hold  objects  at  a 
distance 363 


Page 
Old    people  lose   their 

power  of  walking  392 
spectacles  for  . .   362 
One  pot  will  not  boil  in 

another 113 

how  to  make  it 

boil 114 

Out-of-door  work  pro- 
duces hunger 89 

Owls  prowl  at  night  . .   342 
see  in  the  dark  . .  341 

sleep  all  day 341 

screech  before  rain  1 41 

Oxalic  acid 396 

Oxide  of  copper 233 

iron 231 

lead 234 

Oxide  of  platinum 235 

potassium  . . .  236 

silver 234 

sodium    236 

Oxidised 222 

Oxygen 41 

exhaled!  by  leaves  226 
heats  the  blood . . .  223 

in  the  blood 238 

inhaled 222 

makes  blood  red..  223 
"       fuel  burn..   220 

of  air 96 

'its  use 220 

supports    combus- 
tion   97,  220 

sustains  life 221 

Ozone 35 

Paleness 222 

Palmer's  candles 80 

Paper  burns 46 

not  always  49,  57 

extinguishers 79 

oiled,  transparent.  373 

puckers  from  wet.   317 

used  for  kindling  .     46 

Papillae  392 


474 


INDEX. 


Pa^e 
Paris  plaster  of  454 

Page 

Poison  for  flies  .  .  .           390 

Parlors  smell  of  smoke 
in  summer  71 
Partition  walls  to  arrest 
sound  382 

Poker  draws  up  fire  .  .     56 
hot  against  a  stove  173 
cold  on  a  fender  161  ,  173 
how    to    carry    it 

Pea-soup  fog  207 

when  hot  ....       217 

Peacocks  forebode  rain  141 

Poker  rusts  232 

Pearl  divers  deaf  ....     139 

rust  of    prevented  232 

Polar  current  278 

Perspiration    .  .         88  197 

Polish  use  of                  163 

petals  370 

Polished  metal  tea-pots  184 

Petrels  146 

Ponds  dried  up  153 

Petrifaction  320 

Poor  averse  to  cleanli- 

Phosphate of  lime     .  .   265 

ness  92 

Phosphoric  acid  .  .  ....     43 

Phosphorus  65 

^azy  89 

PHOSPHURFTTED  HYDRO- 

Pores of  wood  105 

GEN  GAS  265 

Porter  froth  of  .  .    107  248 

Piano  fortes  379 

set  before  a  fire  107 

Pickle  tested  335 

Porter,  stale  255 

Pie  with  a  cup  ....       116 

Porter  vats  dangerous  245 

full  of  juice  116 

Positive  electricity  .  .  ,     22 

Pigs  squeak  before  rain  141 

Potatoes    green  372 

Pimpernel     forebodes 

yellow  372 

rain  143 

Potash,  tartrate  of  454 

Pin  puts  a  candle  out     81 

Potassium  236 

Pine  snaps  in  fire  105 
Pipes  broken  by  frost  327 

burns  in  water  236 
Primrose  yellow  ....       371 

Piston  100 

Prisms  divide  light  .  .  .   364 

PLANTS  collect  dew  .  .  .   192 
forebode  rain    •       143 

Psalm  cxlvii.  16,  illus- 
trated      164   311 

grow  out  of  walls  296 
after  moonlight  203 
Plaster  of  Paris  454 

Pump  handle  cold  158 
water  hard  ....  320 
Purple  steel  rusts  233 

of   stoves  falls 
away  •             118 

its    rust    prevent- 
ed    233 

Plasterers  cannot  work 

in  fro^t     .                    334 

differs      from 

Plate  warmer  177,  180 
Platinum  its  use  ....     235 

fermentation  253 
Putrefying  bodies  smell 

never  tarnishes  235 
Ploughing       promotes 
warmth  151 

253,  266 
Quadrupeds  swim  ....  337 

Plumbago  232 

Quick  lime  absorbs  car- 

prevents  rust  232 

bonic  acid  246,  "260 

INDEX.  475 


Page 

Quicksilver  bright ....  '236 

extinguished  454 

Quiet  precedes  storm . .  139 

RADIATION .  182,  228 

cools  iron  ....  228 
Radiators  are    absorb- 
ers    182 

bad 162 

Rags  catch  tire  sponta- 
neously       60 

especially  candle- 
rags  61 

Railway  steamers 201 

water  for 237 

RAIN 313 

affected  by  wind . .  315 

after  lightning 17 

arrests  sound 380 

cause  of 209 

clouds  bode 134 

cools  air 150 

differs  from  dew..  208 
dispels  carb.  acid . .  246 

falls  in  drops 314 

fertilizing....  288,  315 
from  passing  clouds  315 
heaviest  in  summer  318 
least  at  the  poles . .  313 
most  in  mountain- 
ous places 316 

most  in  winter  289,  318 
near  the  equator. .  318 

not  salt 323 

on  dust 206 

cabbages 206 

rose-leaves 206 

prognostics  of 134 

from  animals . . .    L40 
candles  &  fires  141 

clouds 134 

flowers 143 

purifies  air.  : .-  315 

sudden  change  .  . .  302 
RAINBOW 364,  365 


Page 
Rainbow  colors  reversed  367 

Rainbows,  two 366 

Rain  drops 314 

vary  in  size  . .  314 
Rain-water  smells  offen- 
sively     322 

fertilizing 324 

not  salt 323 

soft 321 

stagnant 323 

unpleasant  . . .   322 

Rainy  months 318 

Rare  air  bad  for  sound  383 
Rattling  of  kettle-lid..   112 
Ray  of  light  divided  . .   364 
Reading   aloud  produ- 
ces hunger 88 

RED  color 222,  371 

rose  371 

sky 126,  369 

sun-rise 127,  134 

sun-set 134 

Reflected  light 339 

REFLECTION  of  HEAT  . .   179 

in  a  mirror 345 

in  water 346 

REFLECTORS   179 

help  the  roast  ...   181 
keep  kitchen  cool  181 

not  absorbers 180 

should  be  clean  and 

bright..   177,179 
"  not  be  painted  177 

REFRACTION 358 

Refrangible 126 

Resinous  electricity. . .     23 

Retina 360 

Returning  stroke 23 

Reverberation 383 

Rice  for  food 92 

RIVERS  flow  slowest  at 

sides 324 

freeze  unequally 

328,  380 
invert  our  image  3^6 


476  INDEX. 


Page 
Rivers  never  frozen  at 

bottom 328 

not  wholly  frozen  329 
shallow,     freeze 

fastest 330 

seem  shallower  than 

they  are 359 

warm  if  frozen 330 

Roast  apples 103 

soft 103 

chestnuts 102 

Road  dark  from  a  light 

room 340 

Rocks  collect  no  dew . .   194 
broken  by  frost . . .   326 

Room  cooled 150,  295 

currents  of  air  in  a  270 

ventilated 295 

vitiated  by  a  crowd  295 
warmed  by  fire  . . .   240 

Rose  red 371 

Rosneath,  echo  of 385 

Ross,  Captain 381 

Rotation  of  earth 272 

Rotting  leaves  promote 

cold 152 

Rubbing 98 

Rubbing  hands  to  warm 

them 98 

melts  ice 99 

restores  suspended 

animation 98 

•wood  excites  fire . .     98 
See  friction. 

Ruddiness 223 

Ruins  ftuned  for  echoes  383 
Running       promotes 

warmth 87 

in  a  storm  dan- 
gerous       21 

water  freezes  slow- 
ly     329 

water       makes. 

rough  ice 33 

"  oscillates 324 


Page 

Running  water  pure. . .   324 
Rush  lights  easily  blown 

out 78 

extinguished  by 

a  pin 81 

RUST 231 

prevented 232 

when  most  trouble- 
some     232 

Rustics  healthy 242 

Ruts  frozen 326 

SAFETY    IN    A     STORM 

abroad 25  to  27 

at    a    slight  dis-   * 

tance  from  a  tree  25 
best    to    be    wet    27 

in  a  carriage 26 

in  bed 27 

indoors 26 

Safety  lamp 263 

Sailors  rarely  catch  cold  150 
St.  Bride's  church  de- 
stroyed bv  lightning    30 

SALT ". 454 

and  snow  cold..  39,  332 
and     water     boils 

slowly 114 

crackles  in  a  fire . .     49 
dissolves  ice..  . .  .\   332 
dissolved  by  water  322 
especially  by  hot 

water 323 

flavors  water 322 

of  lemons 454 

retards  boiling.. . .   114 

smelling 454 

white 372 

water  unfit  for  rail- 
way engines . .   237 

for  washing 320 

Salts,  Epsom 396 

Sand  dazzling 374 

Saucepan    boils     best 
when  black 185 


INDEX. 


477 


Page 

Saucepan  boils   slowly 

when  new 185 

lids    should    be 
clean  and  bright  185 

rattle 112 

Scald  cured 14Q 

Scripture  illustrated. . .   16-1 
145, 311 

Scum  of  fermentation..  255 
Sea-beach    healthy    in 

the  morning ....   290 
not  healthy  at  night  290 

Sea  before  storm 139 

gives  out  heat ....  292 
heaves  and  sighs . .  139 
less  hot  than  land.  275 
not  much  heated 

by  sun 275 

Sea-gulls 146 

Sea- vapor  not  salt 154 

Sea-water  easier  to  swim 

in  than  fresh ...  335 
heavy  and  salt ....   323 

rarely  frozen 331 

"      gives  cold..  150 

salt 323 

Sea-waves 292 

Sedentary  pursuits  abate 

hunger 89 

SEEING  in  a  glass 343 

into  a  dark  street.   352 
"      light  room.  340 
.ourselves  in  a  small 
mirror  ....  ....   345 

the  same  object. . .  339 
when  used  to  dark- 
ness    340 

Sensation  destroyed  . .  391 
of  feeling  ...  391 

of  taste 391 

Sewers  purified  by  lime  259 

Shadocool...., 171 

Shadow  in  water. . .  345,  346 
Shadow  larger  as  object . 
approaches  a  light. .   352 


Page 
Shallow     water     soon 

freezes 330 

bleat  before  rain  141 
in  a  storm.     25 
lie  under  hedges  140 

Sheet  lightning 14 

Sheets  wet 149 

Ships  out  at  sea 358 

hull  of,  last  seen  358 

Shirts  of  linen 172 

Shoes  cold  when  wet  . .   148 
hot  when  dusty.   181 

Shot  hot 101 

Shower  cools  air 150 

Shutters  dangerous ...  24 
Sick  rooms  purified.  . .  389 
Sides  of  a  pond  covered 

with  leaves 388 

Sight  affected  by  sud- 
den light 339 

SILVER  meat-covers  . . .    188 
should  not  be 
chased  ...   188 

nitrate  of 454 

tarnishes 234 

Simmering 109 

Simple  clouds 128 

Singing  of  a  kettle 110 

of  boiling  water    110 
produces  hunger    88 
Single  magpie  unlucky  145 
Size  diminished  by  dis- 
tance     354 

Skin,  black,  does   not 

scorch 176 

white  does 179 

itches  before  rain.   142 

Sky  blue 126 

Sleep     elongates     the 

body 390 

body  feels  not  in . .   391 

dreams  in 391 

,  ears  hear  not  in...  391 
eyes  see  no'  in  . . . .  391 
mind  wills  not  in . .  3(^1 


478  INDEX. 


Page 
Sleep,  tongue  tastes  not 

in 391 

Sleet 310 

Slit  chestnuts 103 

Smelling  salts 454 

SMELLS  in  wet  weather  H3 

of  bins  and  sewers  258 

church-yards . . .  265 

putrefying  bodies  253 

SMOKE 45,  62 

ascends '..     62 

curls 62 

falls 144 

"  down  a  chimney    65 

of  fresh  coals 45 

candles 81 

lamps  diminish- 
ed by  a  glass.     83 
red:hot  coals. ..     45 

rises 107 

useful  in  cooking . .  186 

Smoky  chimneys 63 

See  chimney. 

Smoke  jacks 108 

Smouldering  wicks ....     56 

SNOW 309 

arrests  sound 380 

bad  conductor. . . .  311 

cause  of. 310 

falls  in  winter  ....   310 
"   not  in  summer  312 

like  wool 164 

nourishes  the  earth  311 

on  mountains 312 

soon  melts  beneath 
a  hedge  or  wall    191 

use  of 310 

^  warm 310 

mixed    with  salt, 

cold 332 

white 312 

321 

cleansing 321 

hard,  soft 321 

.yellow  321 


Soap-bubbles 368 

ascend 325 

change  color  . . .  368 
Soapy  water  bubbles . .  325 

Soda,  muriate  of 454 

water 247 

"     acid 248 

Sodium  236 

decomposes  water  236 

Soft  soap 321 

water  for  washing  321 

Solids 109 

Sonorous  things 377 

Soot  in  summer 71 

on  ceilings 71 

Sooty  kettles 174 

SOUND 377 

affected  by  frost ..  381 
heat..  381 

arrested  by  mist . .  381 
wet...  380 
diminished  by  rarity 

of  air 383 

heard  best  by  night  381 
in  a  frost  380 
inaudible  on  moun- 
tains     383 

velocity  of 377 

Sounds  musical 377 

prevented  from 
passing  from 
room  to  room  381 

Soup  long  cooling 215 

Sources-  of  heat  . .  9  to  15 
South  wind  rainy  285,  300 

warm 285 

South-east  wind  rainy  286 

Sparks  from  a  lire 105 

aflint....   196 
a      horse- 
shoe ...     97 

Spectacles 361 

black 376 

blue 375 

for  aged 362 


INDEX. 


479 


Page 

Spectacles  for  near  sight  360 

Spectrum 377 

Split  bells 378 

Sponge  swells  when  wet  316 
SPONTANEOUS    COMBUS- 
TION ...   603  84 
of  forests  ...     99 
Spoons  become  dull . . .  234 
bent  in  water ....   359 
discolored  by  eggs  254 
retard  boiling  ...   113 
Speaking  produces  hun- 
ger      88 

Spray  white 371 

Spring,  best  late 288 

crumbles  the  earth  333 

bracing 140 

verdure   372 

Spring  water  cool  ....   171 
"        "        sparkles.  249 
Springs  prevent  freez- 
ing     331 

Sprinkling  to  cool  rooms  150 

Stagnant  water 323 

full  of  worms  323 
Stale  beer,  &c.  (see  beer}  255 
Stars,  distance  and  size 

of 355 

invisible  by  day  . .   342 

seem  flat 356 

seen  in  a  well  ....   342 
seen  on  mountains  350 

twinkle 374 

Starvation 86 

produces  dirtiness  93 
laziness  89 
leanness  86 
madness  86 

STEAM 122 

engines  burst  ....  217 
invisible  ....   112,  216 

ofakettle 216 

"    locomotive.. .  201 
pipes  should  not  be 
black  184 


Page 

Steam,  why  visible 112 

what  becomes  of  it  113 
STEEL  affected  by  light- 
ning      36 

and  flint  make  a 

spark 96 

purple 233 

rusts 233 

prevented  233 
Stick    burnt   makes   a 

circle  of  light 374 

Stillness  before  a  storm  139 
Stirring  cools  broth,  &c.  228 
Stockings  difficult  to 

draw  on  when  wet  . .  317 
STONES  broken  by  frost  326 

cold 159 

collect  no  dew  193 

snap  in  fire 106 

unfit  for  fuel  . .     49 

STORMS 139 

direction  of 34 

distance  of,  told  16,  19 
follow  dry  weather  33 
places  of  danger  in  19 
"  .  safety  in  26 
prevail  in  summer 

and  autumn 33 

rare  in  wet  weather    34 
STOVES     crack     when 

lighted 118 

when   cooling  . .   118 

of  bricks 163 

on  a  floor 54,  217 

rust 240 

most   in    win- 
ter    232 

not  often 232 

prevented 232 

settings  fall  away  118 
smell  of  sulphur . .     59 

smoke 69 

close 62 

warm  a  room  ....     21 
Strataofair 1 


480 


INDEX. 


Fage 
Stratus  clouds     129 

Pare 
Summer  allavs  hunger    91 

Straw  covered,  over  brick- 

clothes for    175 

work  334 

creates  dislike  of 

over  trees     .         334 

grease   .  .         91 

"   water-pipes  334 
Streets  dark  from  a  li°*lit 

"    love  of  fruit    92 
liffhtnin0"      .           17 

room     .      ...    340 

Sun-beams  full  of  motes  228 

seem  to  meet  at 

bottom               354 

-dazzles             .  .       340 

watered       .           150 

dulls  fire          ....     53 

Strikin0"  iron  makes  it 

hot  94 

largest  at  horizon.   350 

Struggling  in  water  dan- 
gerous      .         ....  336 

not  seen  in  a  well.  348 
radiates  heat  183 

Stucco  peels  off  in  frost  333 
Sublimates              .  .       454 

reflected  in  water.   349 
seems  flat  356 

Sublimation             .  .  .     454 

source  of  heat  ....     10 

Sudden  li°-ht  painful    .   339 

Sun-rise  red  127    134 

SUG4R                                                249 

Sun-set  gray  135 

anhydrous        .         250 

red  133    135 

ferments     249 

yellow  133    134 

at  top  of  tea  melts 
quickly  389 

Super-acetate  of  lead  .  .   454 
Suspended     animation 

flavors  water   .  .  .     322 

left  at  tlie  bottom. 

Swallows  fly  low  144 

of  a  cup  melts 
slowly       .      ...   388 

Swan  dry  in  water  206 
Sweet-wort  needs  yeast  252 

makes  alcohol          *^50 

Swimmers  sink   .  .  .         33f> 

"     carbonic  acid  ^50 

Swimmin0*  337 

melted  by  water..   322 
"     especially  by 
hot  water.  322 
of  lead                      454 

in  the  sea  ....  335 
Syrup,  boiling  point  of  115 

Table  salt     454 

retards  boiling  .  .  .  114 
stirred  melts  quick- 
ly                   ...  388 

Tainted  meat  cured  72,  389 
in  moonlight.  203 
water  72 

wh^te                         372 

Tallow      74 

Sulphate  of  lime     320   454 

Tarnish  233 

magnesia     454 

Tartar  emetic    454 

soda  454 

Tartrate  of  potash  454 

zinc  454 

Tarts  have  a  cup  inside  116 

Sulphuric  acid                 454 

full  of  juice  117 

arid  water    37 

Taste     892 

boils  115 
Sumn_er,  air  in  .  .         .  293 

TEA  cooled  by  blowing  228 
by  stirring  228 

INDEX. 


481 


Pa?e 

Tea  cooled  in  a  saucer  153 

green,   deleterious  390 

poison  for  flies  390 

TEA-POT,  bright  metal.   184 

tarnishes  234 

black  earth 184 

preferred  by 

some 184 

set  on  a  hob ....   18'4 

Tea-spoons  tarnished  .  234 

by  eggs  254 

Telescopes 357 

Tempest 139 

affects  weather  305 
Sie  storms. 
Thaumatrope  ....  ....   374 

THAW  affects  barometer  308 

cold 331 

dulls  fire 55 

Theatre  dangerous 25 

Thermometer 119,  296 

Thick     clothing     un- 
healthy    154 

Thread  gloves  cool ....  176 

THUNDER 15 

after  lightning ....     17 
bolts  (see  fulgurites)    1 7 

deep  growl 16 

distance  of,  told.  16,  18 

followed  by  rain . .     17 

wind.     17 

irregular  roar  ....     15 

one  crash 15 

rolling  17 

See  danger,  safety,  storm. 

Tigers  prowl  by  night,  342 

see  in  the  dark.  341 

sleep  all  day  . . .  341 

Tiles  broken  by  frost. .   326 

Timber  charred 73 

Tin-blowers 70 

foot- warmers  . '. . .  162 
"    covered    with 

flannel  162 

plate- warmer  ....  177 


21 


Tin-blowers   reflectors  181 
See  reflectors. 

Tinder  blown 96 

Toast  and  water 73 

dry,  for  the  sick . .  73 

Tomb-stones  frosted  . .  177 

Tongs  rust 232 

prevented..  232 

Tools  hot  from  use  ...  99 

Trade  winds 277,  280 

Transparency 373 

Treble 379 

TREES  barked  by  light- 
ning    34 

collect  dew  190 

covered    with 

bass,  &c 334 

look   more   dis- 
tant in  a  fog..  141 
not  frost-bitten.  211 
promote  warmth  152 

purify  air 242 

shade  of,  cool  . .  171 

Trefoil  forebodes  rain  .  143 

Tube  of  barometer 297 

Tubs  dried  up 153 

Tumblers  (see  glasses.) 

Twilight 370 

Twinkling  of  stars 374 

Two  eyes 343 

"      see  single  ..  343 

logs  burn  best 49 

Unslit  chestnuts 103 

Use  of  barometers 298 

clouds 132 

smoke  in  cooking  186 

snow 310 

Valley  chimneys  smoke  67 

VAPORIZATION 122 

Vapor  a  conductor ....  25 

forms  fog  and 

cloud 209 

of  a  carriage  .  197 


482 


INDEX. 


Page 
Vapor  of  a  room  196 
of  sea   not  salt  154 

Page 
WATER  (see  rain)  319 
and  lime  31    37 

Varnish  to  prevent  rust  232 
Vats  fatal     244 

and  sulphuric  acid    37 
ashes  soften              34^1 

Vegetable  and  animal 
•  life  dependent  225 
Vegetables  absorb  car- 
bonic acid  .  .  .  225 

bad  conductor  161,  214 
boiling..   115,  213,  215 
bubbles  .  Ill,  214 
rattles  112 

agreeable  in  sum- 
mer           91 

runs  over  111 
sings                  109 

collect  dew  192 
cool  the  blood  .  .     92 

cleans  dirty  linen  .  321 
cold  160 

exhale  oxygen  .  224 
Velocity  of  clouds  ....  294 
light  338 

converted  to  steam 
121,  319 
cools  slowly  ...    .     207 

sound  384 

deep  freezes  slowly  330 

wind  ....       294 

dried  up  in  summer  153 

Vent  peg  255 

elastic  253 

expands  by  frost  .  .  327 

sought    by    the 
well-fed     ....     93 

by  heat..   327 
extinguishes  fire  57  106 

sought  not  by  the 
ill-fed  93 
Verdigris      454 

not  always  57.  58 
flat  when  boiled  .  .  257 
fluid  319 

Vertical  sun  273 

flowing  pure  ....     324 

Vinegar  antiseptic  ....  389 
distilled  454 

for  washing..   259,  320 
freezes  at  the  sur- 

Violets blue       371 

face  328 

Violins  musical  378 

fresh,  sparkles  .  .  .  260 

Vitreous    electricity  11,  23 
Vitriol  oil  of    454 

frozen  by  ether  .  .  334 
air-pump  335 

white  454 

fuel  58 

furr  of  237 

Walls  to  arrest  sound     382 

hard  320 

wet  in  winter  ....   199 
"     in  a  thaw  199 
Want   connected  with 
dirt  92 

agreeable  to  drink  260 
unfit   for  washing  320 
how  preserved  cool  179 
hot  179,  187 

Warm  clothes    •  175 

heated  213 

some  things  more 
than  others.  .  .  155 
Warming  rooms    ...       217 

intenses  fire  57 
inverts  images  .  .  .  346 
kept  hot  215 

Wash-hand  basin  160 
Washing  water  for          259 

melts  sugar,   salt, 
&c    322 

should  not  be  hard  320 

especially  hot  373 

INDEX. 


483 


Page 
Water  mixed  with  salt, 

boils  slower 115 

needful  for  ferment- 
ation    255 

not  heated   above 

boiling 215 

of  a  spring  cool  ..   171 

oscillates 324 

pump,  agreeable..  260 

hard 319 

purified   72 

purifies  bins,  &c.  .  259 
reflects  sun  by  a  spot  350 
moon  by  a  path  349 
running,  keeps  pure  324 
salt,  bad  for  wash- 
ing   320 

shallow,       freezes 

fastest 330 

simmers 109 

slackens  flame ....     58 

soft 259,  321 

best  for  washing  321 

sparkles ; . .  249 

stagnant 323 

full  of  worms  323 

stale 257 

swells  with  boiling  110 
will     not    bubble 

without  soap . . .  324 
warm  when  frozen  330 
Water-pipes  broken  by 

frost 327 

covered  with  litter  334 
Watering  plants  by  the 

saucer 388 

streets 150 

Waves 292 

Wax 74 

candles  need  no 
snuffing  ......     80 

Weather    affected    by 

tempests  305 

affected  by  weight 
of  air 297 


Page 

Weather,  prognostics  of  130 
told  by  barometer  296 

rules  for 299 

Weather-toys 317 

Well,  stars  seen  in  ....  348 
sun  not  seen  in  ...  348 

West  winds 201,  285 

Wet  clothes  give  cold  148 

safe 27 

feet  dangerous  ...   148 

finger  cold 148 

indications  of  134  to  136 

kindling 48 

night  oppressive . .  137 

sheets 149 

summer,  cold  win- 
ter    151 

weather    offensive 

137,  140 

Wettest  months 307 

Wheels  catch  fire 98 

greased 98 

kept  cool  by  water  153 
Wheel-ruts  frozen  ....  325 

Wheelwright    117 

WHITK   371 

blisters   178 

body  linen 174 

crust  on  clothes..   154 
dresses  for  summer  175 
"    not  fit  for  win- 
ter    175 

mist.... 138 

vitriol 454 

WICKS,     cotton,     need 

snuffing  80 

gas  of 262 

have  a  nob  when 

long  80 

not  upright  when 

long  80 

Palmer's,  need  no 

snuffing 80 

rekindled  quickly  55, 58 
smoke 81 


484 


INDEX. 


Page 

See  candles. 
Will   o'  the  wisp,  (see 

ignis  fatuus) 266 

WIND 268,  296 

affects  barometer.   299 

"      clouds    125,  127 

after  lightning....     17 

altered  by  clouds . .  276 

"    by  electricity  127 

"    by  seas 275 

always  blows 272 

brings  clouds 182 

"    dry 286 

"     rain 286 

cause  of 268,  272 

changes  the  shape 
of  clouds..  123,125 

cold  171,  184 

dispels  clouds  125,  133 
"      fog...  ....   210 

draws  up  fire 55 

dries  linen 295 

effects  on  air 268 

feels  hot  sometimes  169 
increases  clouds . .  125 
makes  barometer 

fall 299 

makes    chimneys 

smoke "67,  108 

near  mountains.  . .  276 

of  a  morning 289 

of  an  evening 290 

prevents  dew 191 

velocity  of 293 

regular 277 

See  monsoon,  north,  south, 
west,  fyc.,  trade-winds, 

tyc. 
Winding  passages  famed 

for  echoes 384 

Windows  blazing  with 

the  sun 347 

not  at  noon 347 

covered  with  frost  197 

"    mist   196 

carriage,  dull 197 


Windows  rattle 387 

Wine-glasses  (see glasses. ) 
Wine,  fermentation  of  249 
made  without  yeast  254 

Winter  clothing 164 

Winters  less  severe  .  . .   157 

Winter  cold 151 

promotes  hunger    90 

WISDOM  or   GOD   153,  166, 

193,  195,  225,   283,  289. 

328;  3*5 

WOOD  ashes  soften  water  322 

burns 46 

"  spontaneously    59 

charred 72 

hot  at  one  end,  cold 

at  the  other 55 

ignited  by  friction    97 

kindling    47 

"         dry 49 

wet  ....  49 
made  incombustible  49 
sends  forth  sparks  105 

snaps 103 

two  logs  burn  best    49 

will  not  melt 122 

Wooden  handles 156 

Woodpeckers  cry  before 

rain 141 

WOOL  bad  conductor . .  156 
collects  no  dew ..   193 

warm 165,  311 

Woollen  clothing 164 

kettle  holders..   157 
Work  produces  hunger    87 

Yeast 215 

makes  light  bread  275 
not  used  in  wine  215 
used  in  brewing . .   215 
Yellow  flame  gives  best 

light 51 

soap  321 

sun-set  sign  of  wet  133 

Zig-zag  lightning 12 


INDEX  TO  PAET    III. 


Page 
Above  proof    449 

Page 
Books    discolored    by 

Abundance    of  dew  a 

age  423 

sign  of  fine  weather  392 

Brazil  pebbles  438 
Bread    ...             .  .         426 

Acid  stains  removed..  420 

full  of  eyes  399 
hard  from  a°"e      410 

Agate  438 

mouldv  427 

Air  rots  wood  :  .  .      .  .     429 

new  indigestible  410 

Bridges  increase  sound  433 

Ale  443 

Brine  preserves  meat    407 

Alkali  420 

Brown  paper  burns  well  393 

Alkaline  phosphates  .  .  441 
of  meat  407 
Amethyst  438 

sticky  from 
rubbing..  405 
Brown  stout  443 

ANTIDOTES  FOR  POISONS  452 
Apples  sour     .       .         446 

Brushing   hair    makes 
the  head  il  ch            395 

Aqua-fortis,  antidote  for  452 
Arsenic     antidote    for  452 

Burning    glass    ignites 
paper  393 

Burton  ale  443 

Baking     dough      into 
bread  426 

Butter  hard  from  cold  412 
soft  from  heat.  412 

Barometers      measure 
heights                     406 

Cairngorum              .       438 

Bary  tes  45  1 

Candescence.  431 

Beer  443 

Candle  flickering  395 

sour  from  bad  cork- 
ing    444 

Candle-wick  smell  447 
Carbonic  acid  439 

Below  proof  449 

Caries  447 

Binoxide                           394 

Casein  424    443 

Birds  kept  in  feathers  428 
Black  earth  turns  red  402 

Caves  increase  sound.  413 
Cellular  fibre  438 

Blackness  from  decay  419 

Cellulin   414 

Block-tin  451 

Chalcedony  438 

Bloodstones                     438 

Champagne           ...    .  448 

Blue    looks    green  by 
candle-light  393 

Chandelier  lustrous..  .  404 
Chaps  and  chilblains..  402 

Blue  sky  439 

Cheese  *  425 

Boiled  lobster  red  419 
shrimp  red          429 

Chlorate  of  potash  ....  417 
Chloride  of  lime  440 

Boiler  bursts  .  .  .  395 

Chlorine,  antidote  fop.   442 

Boiling  meat                   402 

Chlorophyll           ...       411 

stale  milk   curdles  424 

Chiicky  stone  438 

Boiling'wood  makes  it 
soft...                    .  437 

Churning  makes  butter  425 
Claret  .  .                      ,  .  448 

486 


INDEX. 


Page 

Clothing  warm  if  loose  399 
Clouds  do  not  hide  light  439 

Citric  acid 446 

Citrons  sour 446 

Cold  affects  skin 402 

Color 396 

destroyed  by  dark- 
ness   396 

faded  by  sun 425 

Contagion  prevented..  442 

Copper  bursting v  395 

Copper  cankers 436 

Cork  of  soda- water  flies  401 
pops  401 

Cornelian 438 

shines,  if  wet  397 

Corrosive  sublimate.  ..   440 

antidote  for  453 

Court  buttons 415 

Cream  made  butter. ..  425 

Creasote 444 

for  tooth-ache . . .  447 
to  remove  taint.  444 
Crombs  made  by  boil- 
ing..  437 

Crystal 438 

Cup  filled  beyond  brim  455 
not  if  edge  be  wet  415 

Curdling  milk 423 

Curling     paper     with 

knives 418 

Currants  hard 443 

ripe,  soft 443 

Curtains  promote  heat  397 

Damp  lucifers 417 

of  decay 410 

Darkness  spoils  color.  396 
Decanter-stopple  sticks  418 
Decanting  liquor,  gur- 
gles   416 

Decay,  see  rot. 

black 402 

Decay  of  teeth 447 

theory  of 403 


Dentine 47 

Dextrin 427 

Diastase 427 

Double  doors  increase 
heat 397 

Double    reflexions    in 
glass 438 

Dough 426 

made  bread 426 

Drops  of  water  spread.  406 

Dust  laid  by  night ....  401 

Effervescing  draughts.  420 

Egg  tarnishes  silver. . .  423 

tarnish  removed  by 

salt 422 

Electricity  sticky 405 

Essential  oils 436 

Explosive   lucifers 416 

Explosion  of  gunpowder  442 

Fat  solid 411 

Ficus 448 

Filaments 437 

Fire  destroys  steel-pol- 
ish   413 

revived  by  brush  398 
by  poker  398 

quenched  by  sul- 
phur    421 

warps  wood 425 

Fire-works 451 

Fish  luminous 439 

Fixed  oils 436 

Flag-stones  loose  in  frost  396 
Flickering  of  candles . .  395 

Flint 438 

Flowers  bend  to  sun..  429 
Fog  makes  sun  red ....  393 
Frost  loosens  pavement  396 

Fruit,  antidote  for 453 

Fungus 427 

Glasses  filled  above  brim  415 
not  if  wet 415 


INDEX. 


48T 


Page 
Glazed  pictures  some- 
times invisible  ....  401 
Glazier  mending  a  win- 

Page 
Ink-spots  removed  436 
turn  yellow  394 
Interstices  406 

dow   404 

Iodine    antidote  for        453 

Glue  adhesive  432 

Iris  ornaments  ....         415 

Gooseberries  hard  ....  443 

Iron  bends  430 

soft,  if  ripe  443 

galvanized  450 

hisses  430 

Grapes  sour  446 

melts                       431 

Grease-spots  removed.  436 

rusts  398 

Greasy  paper  unfit  for* 

turns  red  431 

writing  435 

^turns  white  431 

Green  fire-  works   451 

Itch  440 

fruit  hard  443 

Itching  caused  by  hair 

wood  rots  ....       413 

brush                         395 

Grindstone  wet  425 

Guano  438 

Jeweller's  gold  45  f) 

Gum  adhesive  432 

Gunpowder  explosive.  442 
Gurgling  explained...  416 

Knife     sharpened    by 

Gutta  percha  448 

Lactic  acid  424 

Hams  smoked  444 

Lamb  soon  taints  ....     409 

Hard  bread  410 

tender    .  .            408 

soap  445 

Larks  roasted  with  lard  407 

Hartshorn  removes  acid 

Lather  399 

stains  420 

Laudanum  antidote  for  452 

Heat  warps  wood  425 
Hock  448 

Lead  differs  from  solder  450 
Leffumine             .          445 

Horn  shavings  opaque  404 

Lemons  sour  446 

Humus  436 

Hydrate  436 

Light  when  cloudy        439 

of  the  carbonate 
of  copper  ....  436 

Lightning     conductors 
pointed  421 

Ice  in  India  434 

Likeness  reversed  in  a 
glass  417 

Ice-^its  ....  %  434 

Lime  for  manure  .  .  .       438 

Indian  houses  kept  cool  435 
Indian-rubber  448 

Lime-juice  cures  scurvy  440 

erases  pencil  marks  429 

Linen  starched   421 

Indian-  rubber  sticky.  .  405 

Indigo  blue,  white  420 
Infection  prevented  ...  450 

Locomotive  whistle.  .  .  412 
Lucifer  matches  416 

Ink  394 

spoilt  by  damp    417 

Ink-spots  black..       .  394 

Lustres  variegated  ....  403 

488 


INDEX. 


Page 
Manure  for  land  438 

Page 
Oxalic  acid  445 

Marking  ink  449 

antidote  for             452 

Marl  for  manure  ....     438 

removes  ink-spots  436 

Meadows   reverberate.   433 
Meat,     directions     for 
boiling  408 

Oxide  of  potassium  .  .  .  445 
Paint  blisters                   409 

preserved   .  .         444 

preserves  wood     413 

tough  when  old  408 
overcooked  408 
boiled  in  cold 
water  gJ08 
putrefies      from 
change  428 

prevents  rust.  ..   398 
Pannary  fermentation.   410 
Paper  curls  by  scraping  418 
discolored  by  age  423 
Partridges  roasted  with 
lard  .  .  .                  409 

damp  .  .  428 

Paste  adhesive  .  .  .          432 

heat...  427 
Mice  destroyed  442 

Pencil  marks  erased..   429 
Peroxide  394 

Milk  boils  over  400 

of  iron  red       403 

quickly  .  .  .  433 

Pewter  •  450 

burns  432 

Phosphate  407 

curdles  423 

of  lime           440 

by  rennet  424 
sour  from  boiling  424 

of  nieat  407 
Phosphoric  acid  439 

heat...  424 
keeping  424 

Pictures  glazed  invisi- 
ble         451 

Molecules  431 

Plants  bend  to  sun  ....  429 

Moon  shadow  strong  .  .   420 
Mother  of  pearl  414 

Plants  white  if  kept  in 
the  dark.  411 

Mouldy  bread  437 

Plaster  of  walls  peals  off  403 

Mountains  meted  406 
Mutton  fat  hard  .          411 

Points  discharge   elec- 
tricity          .      .  .     422 

Oak  bark  contains  iron  419 
Oak  struck  by  lightning  419 

POISONS,  antidotes  for  452 
Polish  of  steel  destroy- 
ed by  fire  413 

Oar  bent  in  water  392 

Pop-guns  pop  412 

Oil  liquid  411 

Porter,  dark  453 

prevents     water 

Port-  wine  448 

freezing  432 

Potatoes    boiled  422 

thick  in  winter  411 

Proof  spirit  448 

used   on    grind- 

Protoxide  394 

of  iron  black  403 

Oleine...  411 

of  copper  .  .  436 

(Enanthate  447 

Prussic   acid    antidote 

ofethyle..  447 

for  453 

Putty  dancing  404 

Overboiled  meat  toue:h  408 

Putrefaction.  .  .             .  424 

INDEX. 


489 


Page 
Putrid  fish  luminous  .  .  439 
Pyroligneous  acid  ,  444 

Page 
Sesquioxide  of  iron.  .  .  394' 
Shadow  of  moon  and  sun  420 
dark.  443 

Quails  roasted  with  lard  409 

Shear  steel  449 

Quartz  438 

Sherry  448 

Shrill  sounds  412 

Railway  whistle  412 

Shrimps   red  420 

train  passing  a  bridge 

Silent  lucifers  416 

or  meadow  ....       433 

Silica     438 

Rain  brings  .down  cold  435 
Rats  destroyed  442 

Silver  hotter  than  nickel  448 
tarnished  by  egg 

Red  earth  403 

^.Ipanpd    -              422 

by  salt  cleaned  437 

Reflection    in    a    glass 

Sky  blue  439 

double  438 

Small  beer  443. 

reversed  417 
Rennet  425 

Smell  of  sick  rooms  re- 
moved    .  .                442' 

curdles  milk.  ..  424 
Rhubarb  sour  446 

Smelling-bottle  stopple 
sticks  418 

Ripe  fruit  soft  .     .  443 

Smoked  meat   .              444 

Rock  crystal  428 

Soap  made  of  fat     .       445 

Rooms  kept  warm  by 
curtains  397 

Soapy  water  lathers  .  .  .  399 
Soda  in  tea  ....              444 

Rot  413  429    441 

Soda  water  cork  flies  out  402 

Rotting  leaves  hot  410 
Rust  398 

pops  .  .  401 
Soft  soap..  445 

prevented  by  paint  398 

Solder  450' 

Sorrel  sour  445 

Sails  of  mill  turn  ......   396 

Sound  412 

Salt  423 

p    heard      furthest 

beef  produces  scurvy  440 

on  sea  405 

remedy.  .  .  440 
meat  not  nutritious  407* 
meat  needs  vegetables  408 

louder  in  caves.  413 
silenced  by  touch  399 
Sour  milk  424 

removes  tarnish  from 
silver  422 

curdles  423 
Sponge  cleans  a  slate    400 

wine  stains.  ....  442 

Spores  Sporules  ....       427 

tarnishes  silver  .  .  .     437 

Stains  removed       420   436 

tarnishes  removed..  437 
Salts  preserve  meat  .  .  .  407 
wood  ...  414 

Starch  glazes  linen  ....  406 
stiffens  linen  ,  .  .  421 
Stars  twinkle  400 

Sapid  409 

Stearine                   411    445 

Scraped  paper  curls  ...  418 
Scurvy   440   441 

Steel  made  from  iron.  449 
made  brittle          434 

Sea  luminous.  .  .         .  .  440 

Stirring:  a  fire..          .  399  , 

490 


INDEX. 


Page 

Stopples  stick     418 

:                                        Page 
"Vegetables  black  from 
decay  i  .  .  41  9 

Strands     437 

essential  with  salt 
meat      .     ...       408 

Stucco  falls  off                 403 

Sulphate  of  lime  ....       441 

prevent  scurvy  .  .  .   407 
wet  from  decay  .  .  .  403 

soda  423 

Sulphur  quenches  fire.  421 
Sulphuret  of  silver  423 
Sulphuretted  hydrogen  442 

antidote  for..  433 

Volatile  oils  436 

antidote  for  452 
;Sulphurous  acid  4^421 

\yalking-stick  crombs.  437 
Water  388 

.Sugar  of  dough  :  410 
ftSun  fades  colors  426 

freezes  if  exposed  .  431 
sooner  than  milk  431 
when  boiled  432 
hisses  on  fire  430 
rots  wood       •           429 

red  in  fog  393 

warps  wood     «         425 

'Tainted  meat  428 

spreads  on  cloth  ,  .  406 
used  on  grindstones  426 

Tannate  of  iron              436 

Tannic  acid  394,  436 

'Tanning  leather  446 

Wax  hard  409 

Tarnish  of  silver  437 
removed,  423,  437 
of  zinc  436 

liquid..  409,  434 

makes  cotton  strong  437 

or»ff                                                       424 

'Tartaric  acid  446 

Tea  444 

Wet  sponge  cleans  slate  400 
White  lead  450 

improved  by  soda  444 
in  Tartary  4^5 

rushes  to  a  spoon.  415 
Teeth  decav   447 

Whistle  of  locomotive.  412 
Windows  mended  404 

\TT-1            Ml      CQilo                                                      ^QQ 

'Teroxide..*  394 

Tooth-ache,  cause  of..   447 
cure  of.  .  .  447 
Touch  stills  sound  399 
Tough  meat  408 

sour  from  corking  444 
stains  removed  441 

Turpentine       removes 

W^ood  decav  of               441 

flexible,  if  boiled.   437 
preserved  by  paint  413 
by  salts  414 
rotted  by  air  429 
warped  by  heat..   425 

Twinklin0"              .           400 

'Unseasoned  wood  rots  413 

Veal  soon  taints  409 
•tender  408 

Zinc  tarnish.  .'  436 

Testable  fibre..       ,.  414 

14  DAY  USE 

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